Triphosphatrisilacyclohexanes as Tridentate Coronands in Cr and Mo Complexes: Activation of SiH in an Early Stage versus Phosphane Coordination

The SiH bond ousts a phosphorus atom in the coordination to the metal center of the chromium complex 1. This is the surprising result of the reaction of the hexaorganosubstituted P3Si3 ligand 2 with [Cr(CO)3] (• = SiHMes in 1 and 2). The Si,H,Cr three-center two-electron bond in 1 represents a case of very weak SiH activation. The crucial factor determining the unusual complexation is the mesityl substitution at the tiny metal center. This is confirmed by the formation of complexes 3, in which Cr is replaced by Mo and/or mesityl by phenyl groups.