Metalcarbon multiple bonds: synthesis, structure, and electrochemistry of chromium aminocarbyne and phenylcarbyne complexes bearing phosphine or alkyl isonitrile ligands

Abstract The synthesis, structure and cyclic voltammetry studies of neutral and cationic chromium carbyne complexes bearing phosphine or alkyl isonitrile ligands are reported. Treatment of cis -X(CO) 2 (pic) 2 CrCN i Pr 2 (pic: 4-methylpyridine) ( 1a : X  Cl; 1b : X  Br) with two equivalents of PMe 3 and PMe 2 Ph, or one equivalent of 1,2-bis(diphenylphosphino)ethatne (dppe) affords the aminocarbyne complexes cis -Cl(CO) 2 (PMe 3 ) 2 CrCN i Pr 2 ( 2a ). cis -Cl(CO) 3 (dppe)CrCN i Pr 2 ( 2b ) and cis -Br(CO) 2 (PMe 2 Ph) 2 CrCN 1 Pr 2 ( 2e ) respectively. In comparison, reaction of 1a with two equivalents of P(OMe) 3 gives selectively the trans-isomer Cl(CO) 2 [P(OMe) 3 ] 2 CrCN 1 Pr 2 ( 3 ). Complex 2c is converted with TIPF 6 and PMe 2 Ph to the cationic aminocarbyne complex [ fac -(PMe 2 Ph) 3 (CO) 2 CrCN 1 Pr 2 ][PF 6 ] ( 4 ). Similarly, the cationic phenylcarbyne complex [ fac -[ t BuNC) 3 (CO) 2 CrCph][PF 6 ] ( 6a ) is obtained from cis -Br(CO) 2 ( t BuNC) 2 CrCPh ( 5a ), TIPF 6 and t BuNC, Treatment of 1a with four equivalents of isopropyl isonitrile affords the cationic aminocarbyne complex [ cis -( i PrNC) 4 (CO)CrCN i Pr 2 ]Cl ( 9a ), which is converted with TIPF 6 to [ cis -( i PrNC) 4 (CO)CrCN i Pr 2 ][PF 6 ] ( 9b ). Comparative cyclic voltammetry studies of the aminocarbyne complexes 2a, 2c, 4 , cis -Br(CO) 2 ( t BuNC) 2 CrCN i Pr 2 ( 5b ), [ fac -( t BuNC) 3 (CO) 2 CrCN i Pr 2 ][PF 6 ] ( 6b ), mer -Br( t BuNC) 3 (CO)CrCN i Pr 2 ( 7 ), [ cis -( t BuNC) 4 (CO)CrCN i Pr 2 ][PF 6 ] ( 8b ), [( t BuNC) 5 CrCN i Pr 2 IPF 6 ] ( 10 ) and the phenylcarbyne complexes 5a and 6a are reported. The crystal structures of the aminocarbyne complexes 2a and 2c are described.