Bein, Thomas

Cox, Dave E.

Eckert, H.

Herron, Norman

Mac Dougall, Jim E.

Möller, Karin

Stucky, Galen D.

Wang, Ying

English

Open Access LMU ( Ludwig-Maximilians-Univ. München)

8006 J .  Am. Chem. SOC. 1989, 1 1  1 ,  8006-8007 DE-FG02-86ER13564) and the National Science Foundation (Grant DMR 84-17818) for support. R.S. thanks BASF for postdoctoral support, and W.E.C. thanks the National Institutes of Health for a postdoctoral fellowship. We thank K. Knoll for assistance and advice. Registry No. 3t3, 81380-18-9; 4t4, 121987-85-7; 5t5, 121987-86-8; 6t6, W(CH-1-Bu)(NAr)(O-f-Bu),, 107440-84-6; (acetylene)(norbornene) (block copolymer), 121 987-91-5. 121987-87-9; 7t7, 121987-88-0; 8t8, 121987-89-1; 9t9, 121987-90-4; Synthesis and Characterization of 111-V Semiconductor Clusters: GaP in Zeolite Y J. E. Mac Dougall, H. Eckert,* and G. D. Stucky* Department of Chemistry University of California, Santa Barbara Santa Barbara, California 93106 N. Herron and Y. Wang Contribution No. 51 97, Central Research and Development Department E.  I. du Pont de Nemours & Co., Inc. Wilmington. Delaware 19898 K. Moller and T. Bein Department of Chemistry, University of New Mexico Albuquerque, New Mexico 87131 D. Cox Department of Physics Brookhaven National Laboratories Upton. Long Island, New York 1 1  973 Received May 25, 1989 Size quantization effects observed in small semiconductor clusters are currently of great interest for potential nonlinear optic and photocatalytic applications.'-'' While materials based on 11-VI semiconductors have been extensively studied, the prepa- ration of 111-V size quantized semiconductors has been hampered by the much less-developed solution state chemistry in such systems.I2 With the use of inclusion chemistry, we have succeeded in preparing small clusters of GaP in a crystalline, periodic en- vironment of well-defined size and shape (zeolite Y). The reaction (Me)3Ga + PH3 - 3CH4 + GaP was carried out within the p r e s  of Na+/H+ exchanged zeolite Y, by using various loadings of ( Me)3Ga and different reaction temperature and t i m e  with PH3. The synthesis is accomplished by vapor transfer of (Me)3Ga into dry zeolite and slowly warming to room temperature, resulting in CH4 evolution due to the reaction of (Me)3Ga with Bransted acid sites in the zeolite. Excess (Me),Ga and CH, are (1) Henglein, A. Top. Curr. Chem. 1988, 143, 113. (2) Brus, L. J .  Phys. Chem. 1986, 90, 2555-2560. (3) Rajh, T.; Vucemilovic, M. I.; Dimitrijevic, N. M.; Micic, 0. I.; Nozik, A. J .  Chem. Phys. Left. 1988, 143(3), 305-308. (4) Steigerwald, M. L.; Alivisatos, A. P.; Gibson, J. M.; Harris, T. D.; Kortan, R.; Muller, A. J.; Thayer, A. M.; Duncan, T. M.; Douglass, D. C.; Brus, L. E. J. Am. Chem. SOC. 1988, 110, 3046-3050. (5) Wang, Y.; Herron, N.; Mahler, W.; Suna, A. J .  Opt. Soc. Am. E.  1989, 6, 808. (6) Herron, N.; Wang, Y.; Eddy, M. M.; Stucky, G. D.; Cox, D. E.; Moller, K.; Bein, T. J .  Am. Chem. SOC. 1989, 111, 530-40. (7) Moller, K.; Eddy, M. M.; Stucky, G. D.; Herron, N.; Bein, T. J. Am. Chem. SOC. 1989, 1 11, 2564-257 1. (8) Dameron, C. T.; Reese, R. N.; Mehra, R. K.; Kortan, A. R.; Carroll, P. J.; Steigerwald, M. L.; Brus, L. E.; Winge, D. R. Nature 1989,338,596-7. (9) Wang, Y.; Herron, N.  J. Phys. Chem. 1987, 91, 257-260. (10) Henglein, A. J. Chim. Phys. 1987, 84(9), 1043-1047. (11) Gratzel, M. Nafure 1989, 338, 540-541. (1 2) See, for example: Byrne, E. K.; Parkanyi, L.; Theopold, K. Science 1988, 241, 332-334. 1.80E+05 1.60E+05 . 1.20E+05 al 0 1.00E+05 0 .c 4.00E+04 2.00Ec04 O.OOE+OO 200 300 400 500 600 700 800 Wavelength, nm Figure 2. UV-vis spectra of bulk GaP and GaP included in zeolite N a y ,  treated a t  225, 250, and 275 "C in PH,. pumped off at room temperature, and the (Me)3_xGa loaded zeolite is treated with an excess of PH3 for several hours a t  a series of temperatures between room temperature and 400 "C. The product is cooled in vacuum and handled in an inert atmosphere thereafter. The color of samples vary with treatment temperature (white below 200 OC and yellow to orange between 200 and 300 "C), and this change is reflected in the systematic trend seen in the UV-vis spectra. Optical spectra in Figure 2 show a pronounced peak at  290 nm for the low-temperature sample and at  350 nm for the high-temperature samples. These absorption peaks are blue shifted from the band gap of bulk GaP (direct 466 nm, indirect 546 nm). We also note that the 250 O C  and 275 O C  samples absorb to the red of bulk Gap. This may be due to the 0002-7863/89/1511-8006$01.50/0 0 1989 American Chemical Society transformation of an indirect to direct gap, which could be induced by relaxation of the k-selection rule in the quantum confinement regime. This interesting explanation remains to be proven since the possibility of impurity absorption in the tail region has to be rigorously excluded. Bulk chemical analyses (Galbraith Labs., Knoxville, TN) demonstrate that at shorter contact times of PH, (3 h or less) the Ga:P ratio is large (1 1:1, at 300 "C, 3 h) but at longer times (12 h) the ratio is reduced (0.4:1), indicating the presence of unreacted (Me),-,Ga or phosphorus, respectively. X-ray diffraction patterns (both from a lab source and the syn- chrotron) of samples treated at  300 OC and below show no re- flections other than those of the zeolite host (with greatly modified relative intensities due to the inclusion); however, at PH3 treatment temperature of 400 OC, bulk GaP can be identified.', For lower annealing temperatures, the formation of micro- disperse GaP was monitored by ,'P MAS NMR. Figure 2 shows the spectra for four separate samples which had been exposed to (Me),Ga by vapor transport and treated for 3 h in PH, at various temperatures. The sample annealed at 200 OC shows several distinct signals (attributed to molecular precursor complexes) superimposed on a broad resonance (assigned to microdisperse Gap). As the temperature is increased, the sharp peaks disappear, and only the broad resonance, dominated by a distribution of isotropic chemical shifts, remains. Most notably, the center of gravity of the broad resonance is found significantly upfield with respect to bulk GaP (-143 ppm vs 85% H3P04)14 and gradually shifts towards that position with increasing annealing temperature. For the 300 OC sample, the signal has sharpened significantly and resembles that of bulk GaP,I4-l6 whereas the N M R  spectrum of the 400 "C sample confirms the formation of the bulk material. The EXAFS results,I7 for a sample treated at 300 "C with a short PH3 contact time (Le., 3 h), confirm the formation of small GaP clusters most likely located in the supercages of the zeolite.'* Several different shells can be identified by fitting with adequate reference compounds. Ga is present in two distinct coordination environments. About 70% of the Ga is coordinated to the zeolite framework with an average Ga-O bond length of 2.04 A. A peak at about 2.5 A (uncorrected for phase shift) is interpreted as the corresponding Ga-Si/Al scattering from the host lattice. The second environment consists of GaP which is indicated in the EXAFS spectrum and the XANES (X-ray absorption near edge spectroscopy) region of the absorption edge. Three coordination shells of GaP were identified by the fitting procedure: a Ga-P shell a t  2.37 8, (coordination number = 0.9), a Ga-Ga shell at 3.85 8, (CN = l . l ) ,  and a second Ga-P contribution at 4.56 A (CN = 1.5). These bond distances are consistent with those in bulk Gap. The small coordination numbers derived from the fit and the absence of any additional GaP shells indicate the formation of clusters with a size between 10 and 12 A. Further EXAFS and X-ray diffraction experiments are in progress to better elu- cidate the structural nature of the species which are formed. J .  Am. Chem. SOC. 1989, 11 1, 8007-8009 8007 0002-7863/89/1511-8007$01.50/0 0 1989 American Chemical Society (13) J.C.P.D.S. Card Numbers: 12 191 and 32397. (14) Sears, R. E. J .  Phys. Reu. B 1978, 18(7),  3054-3058. (15) Bogdanov, V. L.; Lemanov, V. V. Souiet Physics-Solid Stare 1968, l o ( ] ) ,  2231224. (16) The corresponding ag,7'Ga NMR signals in the disordered low-tem- perature samples are broadened beyond detectability due to quadrupolar coupling. The 300 OC sample exhibits a weak 69Ga MAS NMR signal, which is broadened and shifted due to second-order quadrupolar perturbations, whereas the NMR spectra of the 400 "C sample confirm the formation of the bulk material. (17) EXAFS measurements were performed at the National Synchrotron Lightsource at Brookhaven National Laboratories on beamline X-1 IA with a stored electron energy of 2.5 GeV and ring currents between 100 and 130 mA. Data were collected at the Ga K-edge of 10367 eV at -100 K in transmission mode using a Si( l l1)  channel-cut monochromator. Harmonic contributions were eliminated by detuning the maximum signal -30%. Samples and reference compounds were embedded in a 1:l mixture of ico- sane/octadecane and stored under nitrogen. Thickness of materials was calculated to give a total absorption p <2 5 ,  and data were collected up to 1000 eV over the absorption edge wit$ two scans/sample. Analyses were carried out according to published procedures. (See: Lee, P. A,; Citrin, P. H.; Eisenberger, P.; Kincaid, P. M. Reo. Med. Phys. 1981, 53, 769.) (18) Preliminary Synchrotron X-ray Rietveld data analyses indicate a disordered structure in the supercages of the zeolite. The results thus far indicate that we are able to synthesize small clusters of GaP within the pores of a zeolite and that we can change the optical properties by varying the synthetic conditions. The NMR results confirm the postulated chemistry and the suitability of this technique to monitor the transformation of microdisperse GaP during the synthesis. In conjunction with the UV-vis results and by analogy with the 77Se NMR studies of colloidal CdSeL9 we interpret the chemical shift trend observed in Figure 2 in terms of a systematic change in the average ex- citation energy of Ramsey's paramagnetic chemical shielding contribution as a result of size quantization.*O We therefore propose that, with proper calibration, solid-state NMR chemical shifts can be used to measure the average cluster sizes of such systems. Acknowledgment. G.D.S. and J.E.M. acknowledge the Office of Naval Research and the duPont company for their financial support. Funding by the UCSB Academic Senate (to H.E.) is also gratefully acknowledged. The operational funds for NSLS beamline X-l1A are supported by DOE Grant No. DE- AS0580ER10742. Supplementary Material Available: Figure showing an EXAFS spectrum of sample GaP/NaY 300 OC, magnitude and imaginary parts, Fourier transformed with k3 between 2.8 and 13.1 8,-' (1 page). Ordering information is given on any current masthead page. (19) Thayer, A. M.; Steigerwald, M. L.; Duncan, T. M.; Douglas, D. C. (20) Ramsey, N. F. Phys. Reo. 1950, 78, 669. Phys. Rev. Lett. 1988, 60, 2673-2676. Trapping of the Low-Valent Nitrene Complex (CO),W=NPh with PPh3. Formation of the Phenylnitrene Transfer Product PhN=PPh3 Hanadi F. Sleiman, Suzanne Mercer, and Lisa McElwee-White* Department of Chemistry, Stanford University Stanford, California 94305 Received May 25, 1989 We recently reported the formation of the zwitterion (C0)5WNPhNPhC(OCH3)CH3 (1) as an isolable intermediate in the metathesis reaction of (CO),W=C(OCH,)CH, with photochemically generated cis-azobenzene.' Decomposition of 1 under thermal or photochemical conditions resulted in formation of the organic metathesis product PhN=C(OCH3)CH32 and other compounds apparently derived from the low-valent tungsten nitrene complex (CO),W=NPh (2).3a Many imido complexes have been reported in the l i t e ra t~re .~ .~  However, although species such as the low-valent doubly bonded 2 have been invoked in reaction  mechanism^,^ they have not been directly observed. We now report that thermal decomposition of 1 in the presence of PPh3 results in the trapping of nitrene complex 2 as its phosphine (1) Sleiman, H .  F.; McElwee-White, L. J .  Am.  Chem. SOC. 1988, 110, 8700-8701. (2) Moodie, R. B.; Thomas, P. N.; Schofield, K. J .  Chem. SOC., Perkin Trans. 2 1977, 1693-1705. (3) (a) Geoffroy has also reported the apparent generation of 2 via the metathesis of (CO)5W=C(OCH3)C6H5 with nitrosobenzene. Pilato, R. S.; Williams, G. D.; Geoffroy, G. L.; Rheingold, A. L. Inorg. Chem. 1988, 27, 3665-3668. (b) Low-valent chromium nitrene species have been invoked in the reactions of Fischer carbenes with nitroso compounds and azobenzene. Herndon, J. W.; McMullen, L. A. J .  Orgunomet. Chem. 1989,368, 83-101. Hegedus, L. S.; Kramer, A. Organometallics 1984, 3, 1263-1267. Hegedus, L. S.; Lundmark, B. R., submitted for publication. We thank Prof. Hegedus for providing us with a copy of the latter prior to publication. (4) Nugent, W. A,; Mayer, J. M. Metal-Ligand Multiple Bonds; Wiley- Interscience: New York, 1988. ( 5 )  (a) Nugent, W. A,; Haymore, B. L. Coord. Chem. Reu. 1980, 31, 123-175. (b) Cenini, S . ;  LaMonica, G. Inorg. Chim. Acta 1976, 18, 279-293. 

Synthesis and characterization of group III-V semiconductor clusters: gallium phosphide GaP in zeolite Y

Universität München: Elektronischen Publikationen

8006 J .  Am. Chem. SOC. 1989, 1 1  1 ,  8006-8007 
DE-FG02-86ER13564) and the National Science Foundation 
(Grant DMR 84-17818) for support. R.S. thanks BASF for 
postdoctoral support, and W.E.C. thanks the National Institutes 
of Health for a postdoctoral fellowship. We thank K. Knoll for 
assistance and advice. 
Registry No. 3t3, 81380-18-9; 4t4, 121987-85-7; 5t5, 121987-86-8; 6t6, 
W(CH-1-Bu)(NAr)(O-f-Bu),, 107440-84-6; (acetylene)(norbornene) 
(block copolymer), 121 987-91-5. 
121987-87-9; 7t7, 121987-88-0; 8t8, 121987-89-1; 9t9, 121987-90-4; 
Synthesis and Characterization of 111-V Semiconductor 
Clusters: GaP in Zeolite Y 
J. E. Mac Dougall, H. Eckert,* and G. D. Stucky* 
Department of Chemistry 
University of California, Santa Barbara 
Santa Barbara, California 93106 
N. Herron and Y. Wang 
Contribution No. 51 97, Central Research and 
Development Department 
E.  I. du Pont de Nemours & Co., Inc. 
Wilmington. Delaware 19898 
K. Moller and T. Bein 
Department of Chemistry, University of New Mexico 
Albuquerque, New Mexico 87131 
D. Cox 
Department of Physics 
Brookhaven National Laboratories 
Upton. Long Island, New York 1 1  973 
Received May 25, 1989 
Size quantization effects observed in small semiconductor 
clusters are currently of great interest for potential nonlinear optic 
and photocatalytic applications.'-'' While materials based on 
11-VI semiconductors have been extensively studied, the prepa- 
ration of 111-V size quantized semiconductors has been hampered 
by the much less-developed solution state chemistry in such 
systems.I2 With the use of inclusion chemistry, we have succeeded 
in preparing small clusters of GaP in a crystalline, periodic en- 
vironment of well-defined size and shape (zeolite Y). 
The reaction (Me)3Ga + PH3 - 3CH4 + GaP was carried out 
within the p r e s  of Na+/H+ exchanged zeolite Y, by using various 
loadings of ( Me)3Ga and different reaction temperature and t i m e  
with PH3. The synthesis is accomplished by vapor transfer of 
(Me)3Ga into dry zeolite and slowly warming to room temperature, 
resulting in CH4 evolution due to the reaction of (Me)3Ga with 
Bransted acid sites in the zeolite. Excess (Me),Ga and CH, are 
(1) Henglein, A. Top. Curr. Chem. 1988, 143, 113. 
(2) Brus, L. J .  Phys. Chem. 1986, 90, 2555-2560. 
(3) Rajh, T.; Vucemilovic, M. I.; Dimitrijevic, N. M.; Micic, 0. I.; Nozik, 
A. J .  Chem. Phys. Left. 1988, 143(3), 305-308. 
(4) Steigerwald, M. L.; Alivisatos, A. P.; Gibson, J. M.; Harris, T. D.; 
Kortan, R.; Muller, A. J.; Thayer, A. M.; Duncan, T. M.; Douglass, D. C.; 
Brus, L. E. J. Am. Chem. SOC. 1988, 110, 3046-3050. 
(5) Wang, Y.; Herron, N.; Mahler, W.; Suna, A. J .  Opt. Soc. Am. E.  1989, 
6, 808. 
(6) Herron, N.; Wang, Y.; Eddy, M. M.; Stucky, G. D.; Cox, D. E.; 
Moller, K.; Bein, T. J .  Am. Chem. SOC. 1989, 111, 530-40. 
(7) Moller, K.; Eddy, M. M.; Stucky, G. D.; Herron, N.; Bein, T. J. Am. 
Chem. SOC. 1989, 1 11, 2564-257 1. 
(8) Dameron, C. T.; Reese, R. N.; Mehra, R. K.; Kortan, A. R.; Carroll, 
P. J.; Steigerwald, M. L.; Brus, L. E.; Winge, D. R. Nature 1989,338,596-7. 
(9) Wang, Y.; Herron, N.  J. Phys. Chem. 1987, 91, 257-260. 
(10) Henglein, A. J. Chim. Phys. 1987, 84(9), 1043-1047. 
(11) Gratzel, M. Nafure 1989, 338, 540-541. 
(1 2) See, for example: Byrne, E. K.; Parkanyi, L.; Theopold, K. Science 
1988, 241, 332-334. 
1.80E+05 
1.60E+05 
. 1.20E+05 
al 
0 1.00E+05 
0 
.c 
4.00E+04 
2.00Ec04 
O.OOE+OO 
200 300 400 500 600 700 800 
Wavelength, nm 
Figure 2. UV-vis spectra of bulk GaP and GaP included in zeolite N a y ,  
treated a t  225, 250, and 275 "C in PH,. 
pumped off at room temperature, and the (Me)3_xGa loaded zeolite 
is treated with an excess of PH3 for several hours a t  a series of 
temperatures between room temperature and 400 "C. The product 
is cooled in vacuum and handled in an inert atmosphere thereafter. 
The color of samples vary with treatment temperature (white 
below 200 OC and yellow to orange between 200 and 300 "C), 
and this change is reflected in the systematic trend seen in the 
UV-vis spectra. Optical spectra in Figure 2 show a pronounced 
peak at  290 nm for the low-temperature sample and at  350 nm 
for the high-temperature samples. These absorption peaks are 
blue shifted from the band gap of bulk GaP (direct 466 nm, 
indirect 546 nm). We also note that the 250 O C  and 275 O C  
samples absorb to the red of bulk Gap. This may be due to the 
0002-7863/89/1511-8006$01.50/0 0 1989 American Chemical Society 
transformation of an indirect to direct gap, which could be induced 
by relaxation of the k-selection rule in the quantum confinement 
regime. This interesting explanation remains to be proven since 
the possibility of impurity absorption in the tail region has to be 
rigorously excluded. Bulk chemical analyses (Galbraith Labs., 
Knoxville, TN) demonstrate that at shorter contact times of PH, 
(3 h or less) the Ga:P ratio is large (1 1:1, at 300 "C, 3 h) but 
at longer times (12 h) the ratio is reduced (0.4:1), indicating the 
presence of unreacted (Me),-,Ga or phosphorus, respectively. 
X-ray diffraction patterns (both from a lab source and the syn- 
chrotron) of samples treated at  300 OC and below show no re- 
flections other than those of the zeolite host (with greatly modified 
relative intensities due to the inclusion); however, at PH3 treatment 
temperature of 400 OC, bulk GaP can be identified.', 
For lower annealing temperatures, the formation of micro- 
disperse GaP was monitored by ,'P MAS NMR. Figure 2 shows 
the spectra for four separate samples which had been exposed to 
(Me),Ga by vapor transport and treated for 3 h in PH, at various 
temperatures. The sample annealed at 200 OC shows several 
distinct signals (attributed to molecular precursor complexes) 
superimposed on a broad resonance (assigned to microdisperse 
Gap). As the temperature is increased, the sharp peaks disappear, 
and only the broad resonance, dominated by a distribution of 
isotropic chemical shifts, remains. Most notably, the center of 
gravity of the broad resonance is found significantly upfield with 
respect to bulk GaP (-143 ppm vs 85% H3P04)14 and gradually 
shifts towards that position with increasing annealing temperature. 
For the 300 OC sample, the signal has sharpened significantly and 
resembles that of bulk GaP,I4-l6 whereas the N M R  spectrum of 
the 400 "C sample confirms the formation of the bulk material. 
The EXAFS results,I7 for a sample treated at 300 "C with a 
short PH3 contact time (Le., 3 h), confirm the formation of small 
GaP clusters most likely located in the supercages of the zeolite.'* 
Several different shells can be identified by fitting with adequate 
reference compounds. Ga is present in two distinct coordination 
environments. About 70% of the Ga is coordinated to the zeolite 
framework with an average Ga-O bond length of 2.04 A. A peak 
at about 2.5 A (uncorrected for phase shift) is interpreted as the 
corresponding Ga-Si/Al scattering from the host lattice. The 
second environment consists of GaP which is indicated in the 
EXAFS spectrum and the XANES (X-ray absorption near edge 
spectroscopy) region of the absorption edge. Three coordination 
shells of GaP were identified by the fitting procedure: a Ga-P 
shell a t  2.37 8, (coordination number = 0.9), a Ga-Ga shell at 
3.85 8, (CN = l . l ) ,  and a second Ga-P contribution at 4.56 A 
(CN = 1.5). These bond distances are consistent with those in 
bulk Gap. The small coordination numbers derived from the fit 
and the absence of any additional GaP shells indicate the formation 
of clusters with a size between 10 and 12 A. Further EXAFS 
and X-ray diffraction experiments are in progress to better elu- 
cidate the structural nature of the species which are formed. 
J .  Am. Chem. SOC. 1989, 11 1, 8007-8009 8007 
0002-7863/89/1511-8007$01.50/0 0 1989 American Chemical Society 
(13) J.C.P.D.S. Card Numbers: 12 191 and 32397. 
(14) Sears, R. E. J .  Phys. Reu. B 1978, 18(7),  3054-3058. 
(15) Bogdanov, V. L.; Lemanov, V. V. Souiet Physics-Solid Stare 1968, 
l o ( ] ) ,  2231224. 
(16) The corresponding ag,7'Ga NMR signals in the disordered low-tem- 
perature samples are broadened beyond detectability due to quadrupolar 
coupling. The 300 OC sample exhibits a weak 69Ga MAS NMR signal, which 
is broadened and shifted due to second-order quadrupolar perturbations, 
whereas the NMR spectra of the 400 "C sample confirm the formation of the 
bulk material. 
(17) EXAFS measurements were performed at the National Synchrotron 
Lightsource at Brookhaven National Laboratories on beamline X-1 IA with 
a stored electron energy of 2.5 GeV and ring currents between 100 and 130 
mA. Data were collected at the Ga K-edge of 10367 eV at -100 K in 
transmission mode using a Si( l l1)  channel-cut monochromator. Harmonic 
contributions were eliminated by detuning the maximum signal -30%. 
Samples and reference compounds were embedded in a 1:l mixture of ico- 
sane/octadecane and stored under nitrogen. Thickness of materials was 
calculated to give a total absorption p <2 5 ,  and data were collected up to 
1000 eV over the absorption edge wit$ two scans/sample. Analyses were 
carried out according to published procedures. (See: Lee, P. A,; Citrin, P. 
H.; Eisenberger, P.; Kincaid, P. M. Reo. Med. Phys. 1981, 53, 769.) 
(18) Preliminary Synchrotron X-ray Rietveld data analyses indicate a 
disordered structure in the supercages of the zeolite. 
The results thus far indicate that we are able to synthesize small 
clusters of GaP within the pores of a zeolite and that we can 
change the optical properties by varying the synthetic conditions. 
The NMR results confirm the postulated chemistry and the 
suitability of this technique to monitor the transformation of 
microdisperse GaP during the synthesis. In conjunction with the 
UV-vis results and by analogy with the 77Se NMR studies of 
colloidal CdSeL9 we interpret the chemical shift trend observed 
in Figure 2 in terms of a systematic change in the average ex- 
citation energy of Ramsey's paramagnetic chemical shielding 
contribution as a result of size quantization.*O We therefore 
propose that, with proper calibration, solid-state NMR chemical 
shifts can be used to measure the average cluster sizes of such 
systems. 
Acknowledgment. G.D.S. and J.E.M. acknowledge the Office 
of Naval Research and the duPont company for their financial 
support. Funding by the UCSB Academic Senate (to H.E.) is 
also gratefully acknowledged. The operational funds for NSLS 
beamline X-l1A are supported by DOE Grant No. DE- 
AS0580ER10742. 
Supplementary Material Available: Figure showing an EXAFS 
spectrum of sample GaP/NaY 300 OC, magnitude and imaginary 
parts, Fourier transformed with k3 between 2.8 and 13.1 8,-' (1 
page). Ordering information is given on any current masthead 
page. 
(19) Thayer, A. M.; Steigerwald, M. L.; Duncan, T. M.; Douglas, D. C. 
(20) Ramsey, N. F. Phys. Reo. 1950, 78, 669. 
Phys. Rev. Lett. 1988, 60, 2673-2676. 
Trapping of the Low-Valent Nitrene Complex 
(CO),W=NPh with PPh3. Formation of the 
Phenylnitrene Transfer Product PhN=PPh3 
Hanadi F. Sleiman, Suzanne Mercer, and 
Lisa McElwee-White* 
Department of Chemistry, Stanford University 
Stanford, California 94305 
Received May 25, 1989 
We recently reported the formation of the zwitterion 
(C0)5WNPhNPhC(OCH3)CH3 (1) as an isolable intermediate 
in the metathesis reaction of (CO),W=C(OCH,)CH, with 
photochemically generated cis-azobenzene.' Decomposition of 
1 under thermal or photochemical conditions resulted in formation 
of the organic metathesis product PhN=C(OCH3)CH32 and other 
compounds apparently derived from the low-valent tungsten 
nitrene complex (CO),W=NPh (2).3a Many imido complexes 
have been reported in the l i t e ra t~re .~ .~  However, although species 
such as the low-valent doubly bonded 2 have been invoked in 
reaction  mechanism^,^ they have not been directly observed. We 
now report that thermal decomposition of 1 in the presence of PPh3 
results in the trapping of nitrene complex 2 as its phosphine 
(1) Sleiman, H .  F.; McElwee-White, L. J .  Am.  Chem. SOC. 1988, 110, 
8700-8701. 
(2) Moodie, R. B.; Thomas, P. N.; Schofield, K. J .  Chem. SOC., Perkin 
Trans. 2 1977, 1693-1705. 
(3) (a) Geoffroy has also reported the apparent generation of 2 via the 
metathesis of (CO)5W=C(OCH3)C6H5 with nitrosobenzene. Pilato, R. S.; 
Williams, G. D.; Geoffroy, G. L.; Rheingold, A. L. Inorg. Chem. 1988, 27, 
3665-3668. (b) Low-valent chromium nitrene species have been invoked in 
the reactions of Fischer carbenes with nitroso compounds and azobenzene. 
Herndon, J. W.; McMullen, L. A. J .  Orgunomet. Chem. 1989,368, 83-101. 
Hegedus, L. S.; Kramer, A. Organometallics 1984, 3, 1263-1267. Hegedus, 
L. S.; Lundmark, B. R., submitted for publication. We thank Prof. Hegedus 
for providing us with a copy of the latter prior to publication. 
(4) Nugent, W. A,; Mayer, J. M. Metal-Ligand Multiple Bonds; Wiley- 
Interscience: New York, 1988. 
( 5 )  (a) Nugent, W. A,; Haymore, B. L. Coord. Chem. Reu. 1980, 31, 
123-175. (b) Cenini, S . ;  LaMonica, G. Inorg. Chim. Acta 1976, 18, 279-293. 


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Synthesis and characterization of group III-V semiconductor clusters: gallium phosphide GaP in zeolite Y

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