New 1,2,3-triazole based bis- and trisphosphine ligands: synthesis, transition metal chemistry and catalytic studies

The syntheses and transition metal chemistry of triazole-based bis- and tris-phosphines, 5-(diphenylphosphanyl)-1-(2-(diphenylphosphanyl)phenyl)-4-phenyl-1H-1,2,3-triazole (2), 5-(diphenylphosphanyl)-4-(2-(diphenylphosphanyl)phenyl)-1-phenyl-1H-1,2,3-triazole (5), 1,4-bis(2-(diphenylphosphanyl)phenyl)-1H-1,2,3-triazole (6) and 5-(diphenylphosphanyl)-1,4-bis(2-(diphenylphosphanyl)phenyl)-1H-1,2,3-triazole (7), are described. Bisphosphines 5 and 6 show versatile coordination behavior due to the presence of at least four donor atoms. The reactions of 5 and 6 with group VI metal carbonyl derivatives were found to be highly sensitive to the reaction conditions. Bisphosphine 5 upon treatment with [M(CO)₄(piperidine)₂] (M = Mo and W) yielded both P,P and P,N coordinated complexes [M(CO)₄(5)] [M = Mo-κ²-P,N (8); W-κ²-P,N (9); Mo-κ²-P,P (10); W-κ²-P,P (11)], whereas 6 afforded only P,N coordinated complexes [{o-Ph₂P(C₆H₄){1,2,3-N₃C(o-Ph₂P(C₆H₄))CH}-κ²-P,N}Mo(CO)₄] (12) and [{o-Ph₂P(C₆H₄){1,2,3-N₃C(o-Ph₂P(C₆H₄))CH}-κ²-P,N}W(CO)₄] (13). The reactions of 5 with [M(COD)Cl₂] (M = Pd and Pt) yielded κ²-P,P chelate complexes 14 and 15, respectively, whereas the treatment of 6 with [Pd(COD)Cl₂] at ambient temperature resulted in the formation of a rare fused six-membered PCP pincer complex [{o-Ph₂P(C₆H₄){1,2,3-N₃C(o-Ph₂P(C₆H₄))C}-κ³-P,C,P}PdCl] (16). Similar reactions of 6 with [NiCl₂(DME)] and [Pt(COD)Cl₂] in the presence of LiHMDS yielded [{o-Ph₂P(C₆H₄){1,2,3-N₃C(o-Ph₂P(C₆H₄))C}-κ³-P,C,P}NiCl] (17) and [{o-Ph₂P(C₆H₄){1,2,3-N₃C(o-Ph₂P(C₆H₄))C}-κ³-P,C,P}PtCl] (18), respectively. The reaction between 6 and [M(COD)Cl]₂ (M = Rh and Ir) produced cationic complexes [{o-Ph₂P(C₆H₄){1,2,3-N₃C(o-Ph₂P(C₆H₄))CH}-κ²-P,N}Rh(C₈H₁₂)]Cl (19) and [{o-Ph₂P(C₆H₄){1,2,3-N₃C(o-Ph₂P(C₆H₄))CH}-κ²-P,N}Ir(C₈H₁₂)]Cl (20), respectively, whereas the reaction with [Rh(acac)(CO)₂] resulted in a pincer complex [{o-Ph₂P(C₆H₄){1,2,3-N₃C(o-Ph₂P(C₆H₄))C}-κ³-P,C,P}Rh(CO)] (21). The structures of most of the compounds have been determined by single crystal X-ray analyses. The fused six-membered PCP palladium pincer complex 16 is found to be an excellent catalyst for the Mizoroki-Heck coupling reaction.