Horstmann, Stefan

Schmidpeter, Alfred

Schnick, Wolfgang

English

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Synthesis and Crystal Structure of the First Tetraaminophosphonium Salt P(NH2)4I

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

C O M M U N I C A T I O N S Synthesis and Crystal Structure of the First Tetraaminophosphonium Salt P(NH 2 ) 4 I** Wolfgang Schnick,* Stefan Horstmann, and Alfred Schmidpeter Dedicated to Professor Otto J. Scherer on the occasion of his 60th birthday Unprecedented in chemistry, the acid-base pair H8PN4"7 PN 4 ~ enables structural comparison over a range of eight succes­sive dissociation steps: According to the results of the X-ray struc­ture analysis,161 P(NH 2 ) 4 and I " ions form a CsCl-analogous arrangement in the solid. The P - N bond length (160.7(2) pm) (Fig. 1) represents the shortest P - N H 2 bond distance reported to date. The valence sum for the phosphorus center (5.56), calculat-The characteristic building blocks in phosphorus(v) nitrides are PN 4 tetrahedra. Linkage of these structural elements through common corners allows access to a large number of condensa­tion degrees. This is reminiscent of the varied structural chem­istry of the silicates and phosphates.111 One of the extremes in the series of differently condensed phosphorus nitrides is the ionic compound L i 7 P N 4 , which comprises "isolated" P N ] - ions.121 Due to its extremely high formal charge, no indications for the existence of this anion in solution have yet been found; there­fore, L i 7 P N 4 is accessible only by solid-state reaction of the corresponding binary nitrides. Thus, the certainly high synthetic potential of isolated PN 4 groups in solution for the formation of well-defined Ρ—Ν solid compounds has remained unexplored. The salt L i 7 P N 4 is derived from the hypothetical acid H 7 P N 4 , which is suspected to be an unstable monophosphazene interme­diate during ammonolysis of PC1 5. 1 3 1 However, due to its high basicity and tendency to undergo condensation reactions it has not yet proven possible to isolate imidophosphoric acid tri-amide, H 7 PN 4 . With P(NH 2 ) 4 I (C) we report the first successful synthesis and structural proof of a tetraaminophosphonium salt, which can be regarded as a hydroiodide of H 7 PN 4 . The synthesis followed the modification of a procedure141 that starts from phosphorothionic triamide (A) . t 5 1 Methylation of the sul­phur atom in A with methyl iodide and careful subsequent am­monolysis of Β readily yields the desired product C. As the last NH, CH3I C H N H 2 ; S — Ρ — N H 2 NH 2 Β NH 3 - CH3SH N H 2 H 2 N—P—NHj N H 2 reaction step is a heterogeneous solid-liquid reaction, C is ob­tained as a sparingly-soluble, fine-crystalline powder. The crys­tal growth of tetraaminophosphonium iodide was severely ham­pered by the fact that C is insoluble in most solvents and that, due to its reactivity, it easily undergoes hydrolysis and conden­sation reactions. In the past methanol had been suggested as a solvent for C. However, according to our investigations pro­longed exposure of C to methanol leads to the formation of tetramethylammonium iodide [Eq. (a)]. Sufficiently large single crystals of C were obtained by crystallization from dry aceto-nitrile employing a temperature gradient between 70 °C and room temperature. Obviously, tetraaminophosphonium iodide is sufficiently soluble at the higher temperature. 4 P ( N H , ) 4 I + 4 C H 3 O H — - ( C H 3 ) 4 N I + 4 0 P ( N H 2 ) 3 + 3 N H 4 I (a) I*] Prof. Dr. W Schnick, Dipl.-Chem. S. Horstmann Laboratorium für Anorganische Chemie der Universität D-95440 Bayreuth ( F R G ) Telefax: Int. code + (921)55-2531 Prof. Dr. A. Schmidpeter Institut für Anorganische Chemie der Universität München ( F R G ) [**] This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie. We thank Dr. W. Milius, Universität Bayreuth, for help with and discussion of the X-ray structure analysis. Fig. 1. Structure of the tetraaminophosphonium cation in P(NH 2 ) 4 1. Distances [pm] and angles ["]: P - N 160.7(2), N - H 74.9(26), N-P-N 124.2(2) and 102.7(1), H-N-H 114(3), P-N-H 120(2). ed from the four Ρ—Ν bonds according to O'Keeffe et al. , ( 7 ] is indicative of significant polar bonding or multiple bonds between the phosphorus and nitrogen atoms. The electrostatic repulsion between the nitrogen atoms in P N 4 " (Ρ—N: 171 pm 1 2 1) is obvi­ously compensated by the interaction between the nitrogen atoms and the terminal protons of the tetraaminophosphonium ion. This results in a marked shortening of the Ρ—Ν bonds by approximately 10 pm. In accord with these short Ρ—Ν bond lengths the H-N-H and H-N-P bond angles (114(3)° and 120(2)°, respectively) in the tetraaminophosphonium ion indi­cate a significant Ρ—Ν double-bond character. Even though there are no Ν—Η · · · Ν hydrogen bonds present between the cations, the N H 2 groups are fixed with regard to rotation around the Ρ—Ν bonds. Accordingly, it was possible to locate the positions of the hydrogen atoms unambiguously'81 during X-ray structure analysis by difference-Fourier synthesis. Experimental Procedure S P ( N H j ) 3 (4.53 g, 0.04 mol) was treated with C H 3 I (8.17 g, 0.06 mol) in dry acetoni-trile (25 m L ) for 6 days at room temperature. The resulting solid Β (yield: 76 %) was separated and washed with diethyl ether. 3 I P N M R (36.9 MHz. C D C 1 , , 25 C ) : δ m 48.1 (.ι). Β (4.82 g, 0.02 mol) was suspended in 100 mL of dichloromethane and treated at room temperature (duration: 3 h) with a vigorous stream of N H 3 ( K O H drying column). The resulting solid C was separated off and washed with diethyl ether (yield: 96 % ) . For purification and crystal growth, 1.0 g of C in 25 mL acetoni-trile was transferred to a Schlenk tube, and a temperature gradient (bottom: 70 C. top: 25 °C) was applied to the supernatant. Coarse-crystalline, colorless C deposited at the cooler end. According to X-ray powder diffraction studies and 3 1 P N M R M A S measurements the product was obtained as a single phase. I R ( K B r ) : ν [ α τ Γ ' ] = 3378 (NH) , 3280 (NH) , 3097 (NH) . 1078 (PN), 946 (PN). 7" = 180 C (10 " 3 tnbar, decomposition). All reactions were carried out in dry solvents under an inert argon atmosphere. Received: November 9, 1993 [Z6475IE German version: Angew. Chem. 1994. 106, SIC [1] W. Schnick, /Ingen. Chem. 1993,105,846, Angew. Chem. Int. Ed. Engl. 1993,32 806. [2] W. Schnick, J. Lücke, / Solid Slate Chem. 1990. 87. 101. [3J M. Becke-Goehring, K . Niedenzu, Chem. Ber. 1957, 90. 2072. Angew. Chem. Int. Ed. Engl. 1994. 33. No. 7 (£ VCH Verlagsgesellsihaft mbH. D-69451 Weinheim. 1994 0570-0833/9410707-0785 I 10.00+ .25JO 785 C O M M U N I C A T I O N S [4] A. Schmidpeter. C. Wcingand, Angew. Chem. 1968, 80, 234; Angew. Chem. Int. Ed. Engl. 1968, 7, 210 [5] W. Schnick. Z . Naturforsch. Β 1989, 44, 942. [6J X-ray structure analysis of C : Η β Ρ Ν 4 Ι . Μ m 221.9 gmol" 1 . space group PAinbm. Ζ = 2. a = 842.6(2). c = 486.7(2) pm. V = 345.5 χ 10" pm 3 . ρ^Λ = 2.133 gcm- 3 . f (000) - 208,/ =71.073 pm. 7/ = 173 K . / i ( M o K > ) = 4.76 mm"'. Siemens P4 diffractometer, crystal dimensions (mm): 0.24x0.20x0.20. 2Θ-0 scan, 4.0 ^2fl<60.0' :. 1260 observed reflections. 282 symmetry-independent reflections (K i n , = 0.007), structure solution with direct methods, Η-atoms by difference-Fourier synthesis, structure refinement with full matrix by the least-squares method (16 parameters), all atoms anisotropic, Η-atoms isotropic, R = 0.022, wR = 0.013. Further details of the crystal structure investigation may be obtained from the Fachinformationszentrum Karlsruhe. D-76344 Eg-genstein-Leopoldshafen ( F R G ) . on quoting the depository number C S D -400461 and the journal citation. 17] Ν. E . Brese. M. O'Keeffe, Ada Crystalhgr. Seil. Β 1991, 47, 192. [8] The X-ray structure analysis gave a Ν—Η bond length of 74.9(26) pm. 786 Ο VCH Verlagsgesellschaft mbH. D-69451 Weinheim. 1994 0570-0833/94/0707-0786 $ 10.00 + .25/0 Angew. Chem. Int. Ed. Engl. 1994, 33, No. 7 

Universität München: Elektronischen Publikationen

C O M M U N I C A T I O N S 
Synthesis and Crystal Structure of the First 
Tetraaminophosphonium Salt P(NH 2 ) 4 I** 
Wolfgang Schnick,* Stefan Horstmann, and 
Alfred Schmidpeter 
Dedicated to Professor Otto J. Scherer 
on the occasion of his 60th birthday 
Unprecedented in chemistry, the acid-base pair H8PN4"7 
PN 4 ~ enables structural comparison over a range of eight succes­
sive dissociation steps: According to the results of the X-ray struc­
ture analysis,161 P(NH 2 ) 4 and I " ions form a CsCl-analogous 
arrangement in the solid. The P - N bond length (160.7(2) pm) 
(Fig. 1) represents the shortest P - N H 2 bond distance reported to 
date. The valence sum for the phosphorus center (5.56), calculat-
The characteristic building blocks in phosphorus(v) nitrides 
are PN 4 tetrahedra. Linkage of these structural elements through 
common corners allows access to a large number of condensa­
tion degrees. This is reminiscent of the varied structural chem­
istry of the silicates and phosphates.111 One of the extremes in the 
series of differently condensed phosphorus nitrides is the ionic 
compound L i 7 P N 4 , which comprises "isolated" P N ] - ions.121 
Due to its extremely high formal charge, no indications for the 
existence of this anion in solution have yet been found; there­
fore, L i 7 P N 4 is accessible only by solid-state reaction of the 
corresponding binary nitrides. Thus, the certainly high synthetic 
potential of isolated PN 4 groups in solution for the formation of 
well-defined Ρ—Ν solid compounds has remained unexplored. 
The salt L i 7 P N 4 is derived from the hypothetical acid H 7 P N 4 , 
which is suspected to be an unstable monophosphazene interme­
diate during ammonolysis of PC1 5. 1 3 1 However, due to its high 
basicity and tendency to undergo condensation reactions it has 
not yet proven possible to isolate imidophosphoric acid tri-
amide, H 7 PN 4 . With P(NH 2 ) 4 I (C) we report the first successful 
synthesis and structural proof of a tetraaminophosphonium 
salt, which can be regarded as a hydroiodide of H 7 PN 4 . The 
synthesis followed the modification of a procedure141 that starts 
from phosphorothionic triamide (A) . t 5 1 Methylation of the sul­
phur atom in A with methyl iodide and careful subsequent am­
monolysis of Β readily yields the desired product C. As the last 
NH, 
CH3I 
C H 
N H 2 
; S — Ρ — N H 2 
NH 2 
Β 
NH 3 
- CH3SH 
N H 2 
H 2 N—P—NHj 
N H 2 
reaction step is a heterogeneous solid-liquid reaction, C is ob­
tained as a sparingly-soluble, fine-crystalline powder. The crys­
tal growth of tetraaminophosphonium iodide was severely ham­
pered by the fact that C is insoluble in most solvents and that, 
due to its reactivity, it easily undergoes hydrolysis and conden­
sation reactions. In the past methanol had been suggested as a 
solvent for C. However, according to our investigations pro­
longed exposure of C to methanol leads to the formation of 
tetramethylammonium iodide [Eq. (a)]. Sufficiently large single 
crystals of C were obtained by crystallization from dry aceto-
nitrile employing a temperature gradient between 70 °C and 
room temperature. Obviously, tetraaminophosphonium iodide 
is sufficiently soluble at the higher temperature. 
4 P ( N H , ) 4 I + 4 C H 3 O H — - ( C H 3 ) 4 N I + 4 0 P ( N H 2 ) 3 + 3 N H 4 I (a) 
I*] Prof. Dr. W Schnick, Dipl.-Chem. S. Horstmann 
Laboratorium für Anorganische Chemie der Universität 
D-95440 Bayreuth ( F R G ) 
Telefax: Int. code + (921)55-2531 
Prof. Dr. A. Schmidpeter 
Institut für Anorganische Chemie der Universität München ( F R G ) 
[**] This work was supported by the Deutsche Forschungsgemeinschaft and 
the Fonds der Chemischen Industrie. We thank Dr. W. Milius, Universität 
Bayreuth, for help with and discussion of the X-ray structure analysis. 
Fig. 1. Structure of the tetraaminophosphonium cation in P(NH 2 ) 4 1. Distances 
[pm] and angles ["]: P - N 160.7(2), N - H 74.9(26), N-P-N 124.2(2) and 102.7(1), 
H-N-H 114(3), P-N-H 120(2). 
ed from the four Ρ—Ν bonds according to O'Keeffe et al. , ( 7 ] is 
indicative of significant polar bonding or multiple bonds between 
the phosphorus and nitrogen atoms. The electrostatic repulsion 
between the nitrogen atoms in P N 4 " (Ρ—N: 171 pm 1 2 1) is obvi­
ously compensated by the interaction between the nitrogen 
atoms and the terminal protons of the tetraaminophosphonium 
ion. This results in a marked shortening of the Ρ—Ν bonds by 
approximately 10 pm. In accord with these short Ρ—Ν bond 
lengths the H-N-H and H-N-P bond angles (114(3)° and 
120(2)°, respectively) in the tetraaminophosphonium ion indi­
cate a significant Ρ—Ν double-bond character. Even though 
there are no Ν—Η · · · Ν hydrogen bonds present between the 
cations, the N H 2 groups are fixed with regard to rotation 
around the Ρ—Ν bonds. Accordingly, it was possible to locate 
the positions of the hydrogen atoms unambiguously'81 during 
X-ray structure analysis by difference-Fourier synthesis. 
Experimental Procedure 
S P ( N H j ) 3 (4.53 g, 0.04 mol) was treated with C H 3 I (8.17 g, 0.06 mol) in dry acetoni-
trile (25 m L ) for 6 days at room temperature. The resulting solid Β (yield: 76 %) was 
separated and washed with diethyl ether. 3 I P N M R (36.9 MHz. C D C 1 , , 25 C ) : 
δ m 48.1 (.ι). Β (4.82 g, 0.02 mol) was suspended in 100 mL of dichloromethane and 
treated at room temperature (duration: 3 h) with a vigorous stream of N H 3 ( K O H 
drying column). The resulting solid C was separated off and washed with diethyl 
ether (yield: 96 % ) . For purification and crystal growth, 1.0 g of C in 25 mL acetoni-
trile was transferred to a Schlenk tube, and a temperature gradient (bottom: 70 C. 
top: 25 °C) was applied to the supernatant. Coarse-crystalline, colorless C deposited 
at the cooler end. According to X-ray powder diffraction studies and 3 1 P N M R 
M A S measurements the product was obtained as a single phase. I R ( K B r ) : 
ν [ α τ Γ ' ] = 3378 (NH) , 3280 (NH) , 3097 (NH) . 1078 (PN), 946 (PN). 7" = 180 C 
(10 " 3 tnbar, decomposition). All reactions were carried out in dry solvents under an 
inert argon atmosphere. 
Received: November 9, 1993 [Z6475IE 
German version: Angew. Chem. 1994. 106, SIC 
[1] W. Schnick, /Ingen. Chem. 1993,105,846, Angew. Chem. Int. Ed. Engl. 1993,32 
806. 
[2] W. Schnick, J. Lücke, / Solid Slate Chem. 1990. 87. 101. 
[3J M. Becke-Goehring, K . Niedenzu, Chem. Ber. 1957, 90. 2072. 
Angew. Chem. Int. Ed. Engl. 1994. 33. No. 7 (£ VCH Verlagsgesellsihaft mbH. D-69451 Weinheim. 1994 0570-0833/9410707-0785 I 10.00+ .25JO 785 
C O M M U N I C A T I O N S 
[4] A. Schmidpeter. C. Wcingand, Angew. Chem. 1968, 80, 234; Angew. Chem. Int. 
Ed. Engl. 1968, 7, 210 
[5] W. Schnick. Z . Naturforsch. Β 1989, 44, 942. 
[6J X-ray structure analysis of C : Η β Ρ Ν 4 Ι . Μ m 221.9 gmol" 1 . space group 
PAinbm. Ζ = 2. a = 842.6(2). c = 486.7(2) pm. V = 345.5 χ 10" pm 3 . ρ^Λ = 
2.133 gcm- 3 . f (000) - 208,/ =71.073 pm. 7/ = 173 K . / i ( M o K > ) = 4.76 mm"'. 
Siemens P4 diffractometer, crystal dimensions (mm): 0.24x0.20x0.20. 2Θ-0 
scan, 4.0 ^2fl<60.0' :. 1260 observed reflections. 282 symmetry-independent 
reflections (K i n , = 0.007), structure solution with direct methods, Η-atoms by 
difference-Fourier synthesis, structure refinement with full matrix by the least-
squares method (16 parameters), all atoms anisotropic, Η-atoms isotropic, 
R = 0.022, wR = 0.013. Further details of the crystal structure investigation 
may be obtained from the Fachinformationszentrum Karlsruhe. D-76344 Eg-
genstein-Leopoldshafen ( F R G ) . on quoting the depository number C S D -
400461 and the journal citation. 
17] Ν. E . Brese. M. O'Keeffe, Ada Crystalhgr. Seil. Β 1991, 47, 192. 
[8] The X-ray structure analysis gave a Ν—Η bond length of 74.9(26) pm. 
786 Ο VCH Verlagsgesellschaft mbH. D-69451 Weinheim. 1994 0570-0833/94/0707-0786 $ 10.00 + .25/0 Angew. Chem. Int. Ed. Engl. 1994, 33, No. 7 


German

W. SCHNICK

S. HORSTMANN

A. SCHMIDPETER

ChemInform

ChemInform Abstract: Synthesis and Crystal Structure of the First Tetraaminophosphonium Salt, P(NH2)4I.

http://epub.ub.uni-muenchen.de/3951/1/3951.pdf

Synthesis and Crystal Structure of the First Tetraaminophosphonium Salt P(NH2)4I

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