When Sterics Overcome Electronics: An Unusual Haptotropic P→N Pentacarbonyltungsten Shift
作者:Holger Helten、Gregor Schnakenburg、Jörg Daniels、Anthony J. Arduengo、Rainer Streubel
DOI:10.1021/om1007709
日期:2011.1.10
Acid-induced ring expansion of 2H-azaphosphirene complexes 1a-c with HCN is described. These reactions yielded 2H-1,4,2-diazaphosphole complexes 2a-c as a mixture with their kappa N-coordination isomers 3a-c in different ratios, depending upon the steric demand of the C-3-substituent on the diazaphosphole ring. DFT calculations revealed that the isomerization can proceed in one step via a haptotropic P -> N W(CO)(5) shift. When a mixture of 2b and 3b was heated in acetonitrile, complete decomplexation with formation of 2H-1,4,2-diazaphosphole 5 was observed. Reaction of 2b and 3b with tetra-n-butylammonium fluoride in the presence of [Et3NH][OTf] led to complete desilylation of the P-CH(SiMe3)(2) substituent and formation of complex 6, showing only kappa P-coordination. In addition to NMR, IR, and UV/vis spectra, the single-crystal X-ray diffraction structures of 2a,b and 6 are discussed.