The X-ray crystal structure of the dimer [Cr{H(chba-Et)}(py)_2]_(2)·2py [H_(4)(chba-Et)= 1,2-bis(3,5-dichloro-2-hydroxybenzamido) ethane, py = pyridine] establishes, for the first time, the existence of N-co-ordination of an organic amide to Cr^III, the N-atom and carbonyl O-atom of two separate amide groups being co-ordinated to each Cr^III centre [Cr–N 2.030(6) and Cr–O 1.976(5)Å]; the potentially tetra-anionic chelating ligand leads to a variety of co-ordination modes

Collins, Terrence J.

Santarsiero, Bernard D.

Spies, George H.

English

Caltech Authors - Main

Complexation of Secondary Amides to Chromium(III): the X-Ray

Structure of a Molecule with Two Modes of Monodentate Organic Amide Co-ordination

J. CHEM. SOC., CHEM. COMMUN., 1983 68 1 
Complexation of Secondary Amides to Chromium(rll) : the X-Ray 
Structure of a Molecule with Two Modes of Monodentate Organic 
Amide Co-ordination 
Terrence J. Collins," Bernard D. Santarsiero, and George H. Spies 
Arthur Amos No yes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, 
California 91 125, U.S.A. 
The X-ray crystal structure of the dimer [Cr(H (chba-Et))(py),12.2py [H,(chba-Et) = 1,2-bis(3,5-dichIoro- 
2-hydroxybenzamido)ethane, py = pyridine] establishes, for the first time, the existence of N-co-ordination of 
an organic amide to Crll, the N-atom and carbonyl 0-atqm of two separate amide groups being co-ordinated 
to each Crlll centre [Cr-N 2.030(6) and Cr-0 1.976(5) A]; the potentially tetra-anionic chelating ligand leads 
to a variety of co-ordination modes. 
The co-ordination chemistry of organic amides is an important 
part of a number of current chemical Of con- 
siderable interest is the lowering of reduction potentials of 
metal couples, i.e., stabilization of high oxidation states, that 
accompanies N-co-ordination of the organic amide ligand.1-4 
Our interest in the stabilization of high-valent transition 
metal complexes has led to an exploration of the co-ordina- 
tion chemistry of a new ligand, 1,2-bis(3,5-dichloro-2- 
hydroxybenzamid0)ethane [H,(chba-Et)] (1) (Figure 1 ), 
with a number of metals. The ligand (1) has been designed to 
be reasonably resistant to oxidation, to form five- and six- 
membered chelate rings upon co-ordination, to be easily 
synthesized and derivatized, and to contain the organic amide 
ligating functional group. It is well recognized that co-ordin- 
ation of the organic amide group can occur through the 
nitrogen atom, the oxygen atom, or both.ls5-' We report 
here the crystal structure of an unusual chromium(Ir1) dimer 
in which both possible types of co-ordination are found. This 
is the first structural example of the nitrogen atom from an 
organic amide being co-ordinated to a CrI" metal centre.8 
Chromium trichloride hexahydrate (0.3 g) was added to 
pyridine (50ml) and the mixture was heated under reflux 
until dissolution was complete. 1 equiv. of (1) was added to 
the boiling chromium-py (py = pyridine) solution, and after 
2 min anhydrous sodium carbonate (5  g) was introduced. 
The mixture was stirred for 2min and then filtered. Green 
crystals and a large amount of an amorphous green solid 
formed on leaving the filtrate in a sealed bottle for several 
weeks.? A roughly cubic crystal, edge length ca. 0.25 mm, was 
chosen for the X-ray study; oscillation photographs showed 
a small twin component, but other crystals of suitable size 
were grossly twinned. 
Crystal data: Cs2H48C18Cr2N1008, M = 1448.75, mono- 
clinic, space group P2,/c, a = 14.343(4), b = 14.225(3), 
c = 16.447(8)A, 18 = 104.28(3)", U = 3252(2) A3, 2 = 2, 
Dc = 1.48 g ~ m - ~ ,  p = 7.4 cm-l; data (+h,fk,  fl) were 
collected on a locally modified Syntex P21 diffractometer 
with Mo-K, radiation (A = 0.71069A) up to 28 = 45"; a 
total of 8370 intensity measurements were made with 8-28 
scans. The three standard reflections, remeasured after each 
block of 97 reflections, indicated a 5 %  linear decay over the 
exposure time of 206 h. The data were corrected for decom- 
position, but not for absorption; averaging gave 4279 reflec- 
tions, 3685 with I > 0 and 2031 with I > 3 4 1 ) .  
The positions of the chromium atoms were derived from 
a Patterson map, and the subsequent Fourier and difference 
Fourier maps indicated the locations of the remaining non- 
hydrogen atoms; the hydrogen atoms were placed in calcu- 
lated positions and were not refined. The final cycle of 
refinement gave a goodness-of-fit of 1.38 and R = 0.122 
(RSa = 0.055).$ 
The structure consists of discrete dimers and disordered 
solvent molecules of pyridine. Figure 2 gives bond distances 
about the Cr centres, which are related by a centre of 
symmetry. The distorted octahedral environment includes the 
pyridine nitrogen atoms, an amide nitrogen atom, the phenolic 
oxygen atoms, and an amide-carbonyl oxygen atom; the 
co-ordinated pyridine ligands are cis and the phenolic oxygen 
atoms are trans. 
The carbonyl C-0 bond lengths are equal for both co- 
ordinated and unco-ordinated amide carbonyls 1.278(9) vs. 
1.270(9) A. The Cr-Namide bond length is 2.030(6) A, and 
the two Cr-Ophenol bond lengths are 1.91 5(5) and 1.93 1 (5) A, 
cf., [Cr{N,N'-ethy1enebis(sa1icy1ideneaminato))(H20),]C1 : Cr- 
N 2.005(9) and 1.997(8) A, Cr-0 1.916(8) and I .952(8) A.9 The 
Cr-Ocarbonyl bond length is 1.976(5) A, cf., 1.91(2) 8, found 
in mer-trichloro-(N,N-dimethylformamide)( 1,lO-phenant hro- 
line)chromium(rII).lo The Cr-N,, bond lengths [2.145(6) A, 
trans-to-N and 2.097(6) A, trans-to-0] indicate a greater 
trans-influence of the N-co-ordinated vs. the 0-co-ordinated 
amido ligand. The Cr-Cr distance in the dimer is 8.9A. 
\ 
Ct 
Figure 1. The ligand H,(chba-Et), (1). 
?Important i.r. spectral data (Nujol, crn-l): 3210 [br., w, 
1550 (br., m), and 1505 (br., s) (spectra identical for both 
crystalline and amorphous material). 
v(N-H)], 1605 (s, sh), 1595 (s, Sh), 1580 (sh), 1572 (w, sh), 
$The CRYM computing system was used (D. J. Duchamp, 
California Institute of Technology). Least-squares refinement 
minimized ZwA2 with weights w = ([a(Fa)]' + (0.02 x scan 
counts)2}-1 and A = F t  - FC/k)'. The goodness-of-fit . is 
[Z~A~/(n-p)]~l~,  R = Z 1 F, - \ [ F c / k )  I I /Wo (for reflections with 
I>O) and RS, = R [for reflections with Z>3o(Z)]. The atomic 
co-ordinates from this work are available upon request from the 
Director of the Cambridge Crystallographic Data Centre, 
University Chemical Laboratory, Lensfield Road, Cambridge 
CB2 1EW. Any request should be accompanied by the full 
literature citation for this communication. 
The structure factor table is available as Supplementary Pub- 
lication No. SUP 23676 (26 pp.) from the British Library 
Lending Division. For details of how to obtain this material, 
see Instructions to Authors, J .  Chem. SOC., Dalton Trans., 1983, 
Issue 3. 
682 J.  CHEM. SOC., CHEM. COMMUN., 1983 
Figure 2. Molecular structure of [Cr { H(chba-Et) )(py),],.2py. 
The ambidentate behaviour of the organic amide functional 
group is evident, showing that two types of monodentate 
co-ordination to CrIII are possible, at least where the amide 
is part of a chelating system. In structural investigations with 
metals other than Cr, (1) has been found to co-ordinate 
through the two phenolic oxygen atoms and the two amide 
nitrogen atoms (all to one metal centre). The strong i.r. band 
at 1505 cm-l found for the title dimer is not observed in the 
i.r. spectra of these latter complexes, which exhibit no i.r. 
bands in the 1500-1520 cm-l region. 
We thank the Donors of the Petroleum Research Fund, 
administered by the American Chemical Society, the Research 
Corporation, and the National Science Foundation for 
support of this work. B.D.S. acknowledges support from the 
California Institute of Technology as a Myron A. Bantrell 
Fellow in Chemistry, 1981-1983. 
2 D. W. Margerum, L. F. Wong, F. P. BOSU, K. L. Chellappa, 
J. J. Czarnecki, S. T. J. Kirksey, and T. A. Neubecker, Adv. 
Chem. Ser., 1977, 162, 281. 
3 E. Kimura, A. Sakonaka, and R. Machila, J. Am. Chem. 
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4 A. Buttafava, L. Fabbrizzi, A. Perotti, and B. Seghi, J. 
Chem. SOC., Chem. Commun., 1982, 1 166. 
5 F. A. Cotton, W. H. Ilsley, and W. H. Kaim, J. Am. Chem. 
Sue., 1980,102,3464, 3475; A. Bino, F. A. Cotton, and W. H. 
Kaim, Inorg. Chem., 1979, 18, 3030. 
6 H. C. Freeman, Adv. Protein Chem., 1967, 22, 257; H. C. 
Freeman, ‘Inorganic Biochemistry, Vol. I,’ ed. G. L. Eichorn, 
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7 M. Mulqi, F. S. Stephens, and R. S. Vagg, Inorg. Chim. Acta, 
1981, 51, 9; F. S. Stephens and R. S. Vagg, ibid., 1981, 51, 
149; R. S. Chapman, F. S. Stephens, and R. S. Vagg, Acta 
Crystallogr., Sect. B, 1981, 37, 75. 
8 Incomplete results suggest that VII1 may also replace amide 
protons in similar diphenol-diamide complexes.- See: R. E. 
Banninger, Ph.D. Thesis, University of Basel, Switzerland, 
1967. 
9 P. Coggin, A. T. McPhail, F. E. Mabbs, A. Richards, and 
A. S. Thorley, J. Chem. SOC. A ,  1970, 3296. 
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J. Chem. Suc., Dalton Trans., 1977, 173. 
Received, 23rd February 1983; Corn. 252 
References 
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Complexation of Secondary Amides to Chromium(III): the X-Ray Structure of a Molecule with Two Modes of Monodentate Organic Amide Co-ordination

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