Complexes [{(PwedgeO)PdMe}(n)] (1(n); PwedgeO = kappa(2)-P,O-Ar(2)PC(6)H(4)SO(2)O with Ar = 2-MeOC(6)H(4)) are a single-component precursor of the (PwedgeO)PdMe fragment devoid of additional coordinating ligands, which also promotes the catalytic oligomerization of acrylates. Exposure of 1(n) to methyl acrylate afforded the two diastereomeric chelate complexes [(PwedgeO)Pd{kappa(2)-C,O-CH(C(O)OMe)CH(2)CH(C(O)OMe)CH(2)CH(3)}] (3-meso and 3-rac) resulting from two consecutive 2,1-insertions of methyl acrylate into the Pd-Me bond with the same or opposite stereochemistry, respectively, in a 3:2 ratio as demonstrated by comprehensive NMR spectroscopic studies and single crystal X-ray diffraction. These six-membered chelate complexes are direct key models for intermediates of acrylate insertion polymerization, and also ethylene-acrylate copolymerization to high acrylate content copolymers. Studies of the binding of various substrates (pyridine, dmso, ethylene and methyl acrylate) to 3-meso and 3-rac show that hindered displacement of the chelating carbonyl moiety by pi-coordination of incoming monomer significantly retards, but does not prohibit, polymerization. For 3-meso,3-rac + C(2)H(4) right arrow over left arrow 3-meso-C(2)H(4,) 3-rac-C(2)H(4) an equilibrium constant K(353 K) approximately 2 x 10(-3) L mol(-1) was estimated. Reaction of 3-meso, 3-rac with methyl acrylate afforded higher insertion products [(PwedgeO)Pd(C(4)H(6)O(2))(n)Me] (n = 3, 4) as observed by electrospray ionization mass spectrometry (ESI-MS). Theoretical studies by DFT methods of consecutive acrylate insertion provide relative energies of intermediates and transition states, which are consistent with the aforementioned experimental observations, and give detailed insights to the pathways of multiple consecutive acrylate insertions. Acrylate insertion into 3-meso,3-rac is associated with an overall energy barrier of ca. 100 kJ mol(-1).

Various phosphinesulfonato ligands and the corresponding palladium complexes [{((P^O)PdMeCl)-μ-M}(n)] ([{((X)1-Cl)-μ-M}(n)], (P^O) = κ(2)-P,O-Ar(2)PC(6)H(4)SO(2)O) with symmetric (Ar = 2-MeOC(6)H(4), 2-CF(3)C(6)H(4), 2,6-(MeO)(2)C(6)H(3), 2,6-(iPrO)(2)C(6)H(3), 2-(2',6'-(MeO)(2)C(6)H(3))C(6)H(4)) and asymmetric substituted phosphorus atoms (Ar(1) = 2,6-(MeO)(2)C(6)H(3), Ar(2) = 2'-(2,6-(MeO)(2)C(6)H(3))C(6)H(4); Ar(1) = 2,6-(MeO)(2)C(6)H(3), Ar(2) = 2-cHexOC(6)H(4)) were synthesized. Analyses of molecular motions and dynamics by variable temperature NMR studies and line shape analysis were performed for the free ligands and the complexes. The highest barriers of ΔG(‡) = 44-64 kJ/mol were assigned to an aryl rotation process, and the flexibility of the ligand framework was found to be a key obstacle to a more effective stereocontrol. An increase of steric bulk at the aryl substituents raises the motional barriers but diminishes insertion rates and regioselectivity. The stereoselectivity of the first and the second methyl acrylate (MA) insertion into the Pd-Me bond of in situ generated complexes (X)1 was investigated by NMR and DFT methods. The substitution pattern of the ligand clearly affects the first MA insertion, resulting in a stereoselectivity of up to 6:1 for complexes with an asymmetric substituted phosphorus. In the consecutive insertion, the stereoselectivity is diminished in all cases. DFT analysis of the corresponding insertion transition states revealed that a selectivity for the first insertion with asymmetric (P^O) complexes is diminished in the consecutive insertions due to uncooperatively working enantiomorphic and chain end stereocontrol. From these observations, further concepts are developed.

The coordination strength of various phosphine oxides OPR 3 toward the olefin polymerization catalyst (P ∧ O)PdMe (P ∧ O = κ 2 -P,O-Ar 2 PC 6 H 4 SO 2 O with Ar = 2-MeOC 6 H 4 ) as compared to that of dmso has been determined. Equilibrium constants K L for the reaction 1-dmso + L ⇆ 1-L + dmso range from 3.5 for electron-rich OPBu 3 to 10 −3 for electron-poor OP(p-CF 3 C 6 H 4 ) 3 . Complexes derived from more strongly coordinating phosphine oxides, i.e. [(P ∧ O)PdMe(L)] (1-L; L = OPBu 3 , OPOct 3 , OPPh 3 ) have been isolated and fully characterized. Additionally, 1-OPBu 3 and 1-OPPh 3 were analyzed by X-ray diffraction analyses. Complexes derived from weakly coordinating phosphine oxides have eluded isolation due to loss of phosphine oxide and formation of barely soluble multinuclear palladium complexes 1 n by bridging coordination of the sulfonate group to various Pd centers. Hence, the (P ∧ O)PdMe fragment 1 exhibits an intrinsic limitation with respect to coordination of weak donors. Species 1 generated in situ in the absence of additional ligand (L) has been identified in homo-and copolymerization experiments as well as NMR insertion studies as the most active possible catalyst. Since 1 is generated from the easily available precursor [{(1-Cl)-μ-Na} 2 )], these findings give rapid access to highly active (P ∧ O)PdMe catalysts.

Thirteen different symmetric and asymmetric phosphinesulfonato palladium complexes ([{((X)1-Cl)-μ-M}n], M=Na, Li, 1=(X) (P^O)PdMe) were prepared (see Figure 1). The solid-state structures of the corresponding pyridine or lutidine complexes were determined for ((MeO)2)1-py, ((iPrO)2)1-lut, ((MeO,Me2))1-lut, ((MeO)3)1-lut, (CF3) 1-lut, and (Ph)1-lut. The reactivities of the catalysts (X) 1, obtained after chloride abstraction with AgBF4 , toward methyl acrylate (MA) were quantified through determination of the rate constants for the first and the consecutive MA insertion and the analysis of β-H and other decomposition products through NMR spectroscopy. Differences in the homo- and copolymerization of ethylene and MA regarding catalyst activity and stability over time, polymer molecular weight, and polar co-monomer incorporation were investigated. DFT calculations were performed on the main insertion steps for both monomers to rationalize the effect of the ligand substitution patterns on the polymerization behaviors of the complexes. Full analysis of the data revealed that: 1) electron-deficient catalysts polymerize with higher activity, but fast deactivation is also observed; 2) the double ortho-substituted catalysts ((MeO)2)1 and ((MeO)3)1 allow very high degrees of MA incorporation at low MA concentrations in the copolymerization; and 3) steric shielding leads to a pronounced increase in polymer molecular weight in the copolymerization. The catalyst properties induced by a given P-aryl (alkyl) moiety were combined effectively in catalysts with two different non-chelating aryl moieties, such as (cHexO/(MeO)2)1, which led to copolymers with significantly increased molecular weights compared to the prototypical (MeO)1.