Chemistry of the phosphinophosphinidene tBu2P-P, a novel π-electron ligand -: Review

In reactions with transition metal compounds, (Bu2P)-Bu-t-P=P(X)Bu-t(2) (X = Br, Me) acts mainly as a precursor of the (Bu2P)-Bu-t-P ligand, whereas Bu-t(Me3Si)P-P=P(Me)Bu-t(2) acts as a precursor of the (Me3Si)P=(PBu)-Bu-t ligand. Up to now, only Pt(0) d(10) ML2 metal centres were found to be able to stabilize the (Bu2P)-Bu-t-P group in 'pure form' by means of eta(2)-coordination (side on). Several compounds of the [{eta(2) -(Bu2P)-Bu-t-P}Pt(PR3)(2)] type were sufficiently stable to be isolated and characterized; however, not all of them gave single crystals suitable for X-ray structure determinations. The X-ray structures of these compounds and of [{mu - (1,2:2 - eta -(Bu2P)-Bu-t-P)Pt(PR3)(2)} {M(CO)(5)}] strongly suggest the ethenelike form of 1,1-di-tert-butyldiphosphene in these complexes. Such a form is also in agreement with RI DFT calculations with SVP basis for free (Bu2PL)-Bu-t-P. However, in trapping experiments with cyclic olefins and cyclic dienes (Bu2P)-Bu-t-P exhibits, to some extent, electrophilic 'singlet carbene' properties. Copyright (C) 2002 John Wiley Sons, Ltd.