Diphosphine substitution in pentakis(arylisocyanide)cobalt(I) complexes; 31P NMR, cyclic voltammetric and ESI mass spectrometry studies

Five new complexes of the type [Co(CNC6H3iPr2-2,6)4PPh2-R′-PPh2]X, X = BF4, ClO4; R′ =–(CH2)2– (1), –(CH2)3– (2), –CHdouble bond; length as m-dashCH-trans (3), –Ctriple bond; length of mdashC– (4) and –C6H4-p (5); and two new bimetallic complexes, [{Co(CNC6H3iPr2-2,6)4}2(μ-PPh2(CH2)3PPh2)](ClO4)2 (6) and [{Co(CNC6H3iPr2-2,6)4}2(μ-PPh2C6H4PPh2-p)](ClO4)2 (7), have been synthesized and characterized by various spectroscopic methods.Known monometallic and bimetallic complexes bearing the ligand CNC6H3Et2-2,6 instead of CNC6H3iPr2-2,6 have been included in the 31P NMR, cyclic voltammetric and mass spectrometry studies.Comparison of the CNC6H3iPr2-2,6 with the CNC6H3Et2-2,6 complexes shows that the increased steric bulkiness of the former makes it more suitable for synthesis of the monometallic complexes, whilst the CNC6H3Et2-2,6 is more apt to give bimetallic complexes.Thus, the two arylisocyanides are complementary with respect to synthesis of the monometallic and bimetallic complexes.The 31P NMR indicates that the diphosphines in monometallic complexes behave as non-fluxional, monodentate ligands at ambient temperature, with 31P–31P coupling shown for the PPh2CH2PPh2, PPh2(CH2)2PPh2 and PPh2Ctriple bond; length of mdashCPPh2 ligands. Cyclic voltammetry fails to show electronic communication in the bimetallic complexes, and mass spectrometry indicates significantly greater stability for fragments containing potentially chelating diphosphines as compared to diphosphines that cannot chelate.