Simultaneous End-On/Side-On Coordination Modes of a Diphosphorus Tetrahedral Complex Imposed by Pre-organization of Oligometallic CuI Acceptors

The reaction of the [{CpMo-(CO)(2)}(2)(mu,eta(2):eta(2)-P-2)] (Cp=cyclopentadienyl) metallo-ligand 2 with pre-organized Cu-I bi- and trimetallic precursors afforded new coordination complexes with unprecedented coordination modes for a Mo2P2 complex. Variable-temperature solution and solid-state P-31 NMR spectroscopy measurements were performed and Xray diffraction studies revealed an eta(2):eta(1) coordination mode for the Mo2P2 unit of 2 in the Cu-I bimetallic complexes 3 and 4. DFT calculations were carried out to highlight the bonding situation of this unprecedented coordination mode in the CuI bimetallic compound 3. It is built up from a side-on coordination of the P-P sigma bond to one copper ion and from the interaction of the lone pair of one phosphorus atom with the second copper ion. The remaining available lone pair of the second phosphorus atom can be involved as well to interact with an additional metal centre, as evidenced in the Cu-I trimetallic compound 5 in which an eta(2):eta(1):eta(1) coordination mode of the ligand 2 is observed. Derivative 3 can be used as a molecular clip to obtain discrete pi-stacked dimers through a ligand exchange reaction between acetonitrile ligands and cyano-capped pi-conjugated systems, indicating the stability of the new eta(2):eta(1) coordination mode.