Review: Chemistry of the phosphinophosphinidene t Bu 2 PP, a novel π‐electron ligand

In reactions with transition metal compounds, t Bu 2 PPP(X) t Bu 2 (X = Br, Me) acts mainly as a precursor of the t Bu 2 PP ligand, whereas t Bu(Me 3 Si)PPP(Me) t Bu 2 acts as a precursor of the (Me 3 Si)PP t Bu ligand. Up to now, only Pt(0) d 10 ML 2 metal centres were found to be able to stabilize the t Bu 2 PP group in ‘pure form’ by means of η 2 ‐coordination (side on). Several compounds of the [{η 2 − t Bu 2 PP}Pt(PR 3 ) 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 [{µ − (1,2:2 − η − t Bu 2 PP)Pt(PR 3 ) 2 } {M(CO) 5 }] strongly suggest the ethene‐like 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 t Bu 2 PP. However, in trapping experiments with cyclic olefins and cyclic dienes t Bu 2 PP exhibits, to some extent, electrophilic ‘singlet carbene’ properties.