Halfsandwich Carbonylmetal Complexes of Vanadium,Chromium, and Manganese Containing Tri(1‐cyclohepta‐2, 4, 6‐trienyl)phosphane,P(C7H7)3

The photo‐induced substitution of a CO ligand has been used to prepare the halfsandwich complexes (η³‐C₃H₅)V(CO)₄P(C₇H₇)₃] ( 1 ), (η⁵‐C₅H₅)V(CO)₃P(C₇H₇)₃] ( 2 ), (η⁷‐C₇H₇)V(CO)₂P(C₇H₇)₃] ( 3 ), (η⁶‐C₆H₃Me₃)Cr(CO)₂P(C₇H₇)₃] ( 4 ), and (η⁵‐C₅H₅)Mn(CO)₂P(C₇H₇)₃] ( 7 ), in which the olefinic phosphane is coordinated as a conventional two‐electron ligand through the lone pair of electrons at phosphorus. Some analogues, which are permethylated at the aromatic ring ( 2* , 4* , 7* ), were included for comparison. Subsequent photo‐elimination of another CO group from 4 or 7 converts the olefinic phosphane into a chelating four‐electron ligand, leading to (η⁶‐C₆H₃Me₃)Cr(CO)P(C₇H₇)₂(η²‐C₇H₇)] ( 5 ) and (η⁵‐C₅H₅)Mn(CO)P(C₇H₇)₂(η²‐C₇H₇)] ( 8 ), respectively. The η²‐coordinated double bond in 5 and 8 can be displaced by trimethylphosphite to give (η⁶‐C₆H₃Me₃)Cr(CO)P(C₇H₇)₃]P(OMe)₃] ( 6 ) and (η⁵‐C₅H₅)Mn(CO)P(C₇H₇)₃]P(OMe)₃] ( 9 ). The ³¹P and ¹³C NMR spectra of all complexes are discussed, and X‐ray structure analyses for 2 and 8 are presented. Prolonged irradiation of 7 and 8 led to a di(cycloheptatrienyl)phosphido‐bridged dimer, {(η⁵‐C₅H₅)Mn(CO)P(C₇H₇)₂]}₂( 10 ).