Palladium Complexes of C₂-, C₃-, and C₄-Bridged Bis(phospholyl) Ligands:  Remarkably Active Catalysts for the Copolymerization of Ethylene and Carbon Monoxide

Abstract

The C2-, C3-, and C4-bridged bis(2,3,4,5-tetramethylphospholes) (1a, X = C2H4; 1b, X = C3H6; 1c, X = (CH2)2C6H4) and their corresponding palladium complexes [(P-P)PdCl2] (2a−c) have been prepared and characterized. A single-crystal X-ray analysis of [{bis(2,3,4,5-tetramethylphospholyl)-o-xylene}PdCl2] (2c) reveals that 1c forms a seven-membered chelate; the phosphole rings are oriented perpendicular to the PdP2Cl2 plane. Methanol solutions of [(P-P)Pd(OAc)2] (3a, P-P = 1b; 3b, P-P = 1c) and methanesulfonic acid are active for the copolymerization of ethylene and carbon monoxide, generating high-molecular-weight polymers with narrow molecular weight distributions. Under our conditions, the activity of catalyst systems containing 1c is comparable to that based on bis(diphenylphosphino)propane (dppp).

Alternating and Non‐Alternating Pd‐Catalysed Co‐ and Terpolymerisation of Carbon Monoxide and Alkenes

“…[10] Experimental evidence has also shown that four-membered ring systems with isopropyl-substituted phenyl rings can also exhibit high catalytic activity (Figure 4). [11] Phosphorus-metallocene based ligands have also been tested recently for the copolymerisation of CO/ethene.…”

The Continuing Development of the Chemistry of Phospholes

“…A bis-phosphonous dichloride (14) has been reacted with zirconacyclopentadiene 3 to give a 1,1-bridged bisphosphole (Equation 7 ) [13], demonstrating further versatility of the Fagan-Nugent method.…”

“…The metals with pertinent references given in parentheses are: Co [118], Cr [78], Fe [8,9,28,34,42,74,119,120,121,122,123], Ga [8], Ge [124], Hf [125], Ir [126,127], Mn [28,74,128,129,130,131], Mo [132], Nd [9], Pb [124], Pd [11,13,17,28,66,67,68,69,70,71,133,134,135,136,137,138,139], Pt [11,28,69,72,133,134,…”

Metal‐Catalyzed Synthesis of Alternating Copolymers

“…[32] The beneficial effect of the ligand rigidity on copolymerization reactions has also been confirmed by Doherty et al, with bis-phospholyl substituted carbon backbones. [33] Dossett et al provided experimental evidence that four-membered ring systems with i-propyl substituted phenyl rings exhibit high catalytic activity. [34] More recently, palladium complexes supported by metallocene-based ligands such as 4-7 have been tested in the copolymerization reaction of CO and ethylene ( Figure 2).…”