73789-72-7Relevant academic research and scientific papers
Free and metal-coordinated (N-isocyanimino)triphenylphosphorane: X-ray structures and selected reactions
Stolzenberg, Heribert,Weinberger, Bernd,Fehlhammer, Wolf Peter,Puehlhofer, Frank G.,Weiss, Robert
, p. 4263 - 4271 (2005)
An improved procedure for the synthesis of (N-isocyanimino)- triphenylphosphorane, C≡N-N=PPh3 (3), is described. The X-ray structure analysis reveals an unusually small N-N=P angle [115.2(2)°] and an N-N bond order of only about 1.5, which indicates considerable C≡N-N --P+ participation and electronically more-isolated functional groups (CN, P=N) in the isocyanide than, for example, in the isomeric N≡C-N=PPh3 (4) [C-N=P = 123.0(4)°, C-N bond order = 2.0]. In order to gain insight into the stereochemical consequences of metal coordination of 3, an X-ray structural study of [Cr-(CO)5C≡N-N= PPh3] (5) was also undertaken. Surprisingly, the central bond lengths (C-N, N-N) and angles (C-N-N) remain practically unchanged with noticeable coordination effects occurring only at the periphery of 5, with the N-N-P angle [112.3(2)°] further decreased by 15σ, the elongated (by 7σ) P-N bond, the somewhat shortened (by 4σ) P-C(Ph) bonds and even shorter C-H(Ph) bonds on the one side, and the well-known Cr-C(O)trans contraction on the other. Treatment of 5 or its tungsten derivative with anhydrous Bronstedt and Lewis acids such as CF3COOH, HCl, COS, phosgene or, most efficiently, [PdCl2(1,5-COD)] causes CN→NC isomerisation to give [M(CO)5N≡C-N=PPh3] [M = Cr (6), W (7)]. In solution, [PdCl2(CNNPh3)2] and Ph3BCNNPPh3 (8) slowly isomerize even without additional acid to give both free and Pd-coordinated 4 and Ph3BNCNPPh 3 (9), respectively. In the presence of catalytic amounts of [PdCl2(1,5-COD)], 3 is converted into 4 and the dimer Ph 3PN-C(CN)=N-NPPh3 (10) in an almost 1:1 ratio. The optimised geometries of the methyl derivatives of 3 and 4, namely Me 3P=N-N≡C (3c) and Me3P=N-C≡N (4c), are in excellent agreement with the experimental data; major differences between the isomers (P-N-N angle, N-N bond length) are explained by the higher electronegativity of the isocyano group as compared to the CN substituent, which, in turn, is a better π-acceptor). The reaction path of the isomerisation of 3 to 4 (3c to 4c) has also been studied computationally and been found to proceed via an [(P)=NA-N≡CA(N A-CA)] cyclic transition state. The overall process is exothermic by 50 kcal mol-1. Wiley-VCH Verlag GmbH & Co. KGaA, 2005.
