PUB - Publikationen an der Universität Bielefeld

The olefinic C-H bond functionalization of (NHC)CHPh (NHC = IPr = C{(NAr)CH}c2 1; SIPr = C{(NAr)CH2}2 2; Ar = 2,6-iPr2C6H3) derived from classical N-heterocyclic carbenes (NHCs) with PCl3 affords the dichlorovinylphosphanes {(NHC)C(Ph)}PCl2 (NHC = IPr 3, SIPr 4). Two electron reduction of 3 and 4 with magnesium leads to the formation of the divinyldiphosphenes [{(NHC)C(Ph)}P]2 (NHC = IPr 5, SIPr 6) as crystalline solids. Unlike literature known diphosphenes, which are mostly yellow or orange, 5 is a green whereas 6 is a purple solid. While the P=P bond lengths of 5 (2.062(1) A) and 6 (2.055(1) A) are comparable with those of the known diphosphenes (2.02-2.08 A), the C-P bond lengths of 5 (1.785(1) A) and 6 (1.797(1) A) are, however, considerably shorter than a C(sp2)-P single bond length (1.85 A), indicating a considerable pi-conjugation between C=C and P=P moieties. The HOMO-LUMO energy gap for 5 (4.15 eV) and 6 (4.52 eV) is strikingly small and thus the narrowest among the diphosphenes (> 4.93 eV) reported as yet. Consequently, 5 readily undergoes P=P bond cleavage at room temperature on treatment with sulfur to form the unique dithiophosphorane {(IPr)C(Ph)}P(S)2 7. Interestingly, reaction of 5 with selenium gives the selenadiphosphirane [{(IPr)C(Ph)}P]2Se 8 with an intact P-P bond. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.