Bis(diphenylphosphino)methane-Phosphonate Ligands and Their Pd(II), Ni(II) and Cu(I) Complexes. Catalytic Oligomerization of Ethylene

Abstract

The bis(diphenylphosphino)methane-phosphonate-based (dppm-phosphonate) ligands (Ph(2)P)(2)CHP(O)(OR)(2) (R = Me, L(1); R = Ph, L(2)) form metal complexes by selective coordination of the diphosphine moiety to Pd(II) and Ni(II) centers. The formation of complexes containing the chelating, deprotonated form of ligand L(1) or L(2) occurred when basic ligands were present in the precursor complex, such as Me or dmba (on Pd(II)) or acac (on Ni(II)). The Cu(I) complex [CuL(1)](2)(BF(4))(2) (9) was obtained that is suggested to be dinuclear, each Cu(I) being chelated by a phosphine and a P=O donor and further bound to the phosphine group of another ligand. The crystal structures of the mononuclear complexes [PdCl(2){(Ph(2)P)(2)CHP(O)(OMe)(2)-P,P}] (2a), [PdCl(2){(Ph(2)P)(2)CHP(O)(OPh)(2)-P,P}] (2b), [Pd{(Ph(2)P)(2)CP(O)(OMe)(2)-P,P}(2)] (6a) in 6a.2CH(2)Cl(2), [Pd{(Ph(2)P)(2)CP(O)(OPh)(2)-P,P}(2)] (6b), [Ni{(Ph(2)P)(2)CP(O)(OMe)(2)-P,P}(2)] (10a) in 10a.4CHCl(3), [Ni{(Ph(2)P)(2)CP(O)(OPh)(2)-P,P}(2)] (10b) in 10b.4CHCl(3), [NiCl(2){(Ph(2)P)(2)CHP(O)(OMe)(2)-P,P}] (11a) in 11a.CHCl(3) and of the dinuclear complexes [Pd(mu-Cl){(Ph(2)P)(2)CP(O)(OMe)(2)-P,P}](2) (7a) and [Pd(mu-Cl){(Ph(2)P)(2)CP(O)(OPh)(2)-P,P}](2) (7b) have been determined by X-ray diffraction. The complexes [Ni{(Ph(2)P)(2)CC(O)NPh(2)-P,P}(2)] (13) and [Ni{Ph(2)PC(Ph)P(O)(OEt)(2)-P,O}(2)] (15) were prepared by reaction of [Ni(acac)(2)] with the known, neutral ligands (Ph(2)P)(2)CHC(O)NPh(2) and Ph(2)PCH(Ph)P(O)(OEt)(2), respectively. The Ni(II) complexes were evaluated for the catalytic oligomerization of ethylene and afforded similar results when AlEtCl(2) was used as cocatalyst. Complexes 11a,b were the most active, with a turnover frequency (TOF) of 78 300 mol of C(2)H(4)/(mol of Ni)h) for complex 11b in the presence of 10 equiv of AlEtCl(2) and showed a high selectivity for C(4) and C(6) olefins with up to 93% C(4) for 10a in the presence of 6 equiv AlEtCl(2), whereas when only 3 equiv cocatalyst was used with 10a, 64% trimers were observed. In the presence of methylalumoxane (MAO) as cocatalyst, precatalysts 10a,b, 11a,b, and 15 gave moderate TOFs, up to 11,660 mol of C(2)H(4)/(mol of Ni)h) for complex 11a with 400 equiv of MAO. Mostly ethylene dimers were formed but up to 39% trimers were observed with 10a in the presence of 400 equiv MAO.

Synthesis, Structure, and Optical Properties of Pt(II) and Pd(II) Complexes with Oxazolyl- and Pyridyl-Functionalized DPPM-Type Ligands: A Combined Experimental and Theoretical Study

“…For the PCP-pyridine complexes, the emission spectra are mostly 3 LMCT and not ligand-centered in character, as the emission wavelengths for both the Pt(II) and Pd(II) complexes are strongly bathochromically shifted by 3350 and 6100 cm −1 for 5a and 5b, respectively, with respect to the emission of the free deprotonated ligand (present work, 478 nm; also see ref 23). Indeed, the theoretical analysis indicates that the lowest states contributing to the emission band have LMCT character with an electronic distribution very similar to that of the lowest-energy S 1 and T 1 transitions.…”

“…23 Spontaneous deprotonation of these ligands at the PCHP site occurred when a basic ligand was present in the precursor metal complex, such as 2-{(dimethylamino)methyl}phenyl-κ 2 -C 1 ,N (dmba) or methyl in the case of Pd(II) or acac in the case of Ni(II).…”

Recent advances in Ni-mediated ethylene chain growth: Nimine-donor ligand effects on catalytic activity, thermal stability and oligo-/polymer structure

“…By contrast, pyridinylimine-based N^N-nickel pre-catalysts, in the main, promote the conversion of ethylene to α-olefins with the ligand structure, substitution effects and process conditions playing an important role on the catalytic activity and product distribution [24,25,29]. Elsewhere, Braunstein and co-workers have made significant contributions in the field of catalytic ethylene oligomerization [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] and, in particular, with regard to the preparation and application of P^N [30][31][32]34,36], P^P [38,40], N^P^N [37] and SHOP-type [35,38] nickel complexes for olefin oligomerization. In general, however, it still remains difficult to achieve performance characteristics that can compete with industrial catalysts.…”

Paradox of Late Transition-Metal Catalysts in Ethylene Polymerization

“…Notably, the formation of hyperbranched polyethylenes by nickel catalysts displaying properties characteristic of thermoplastic elastomers shows great promise for these materials to be employed as alternatives to elastomeric ethylene copolymers. [25][26][27] With regard to the preparation and application of nickel catalysts, a large number of studies have started from the modification of α-diimine ligand to form an extension of the bidentate N^N system to P^N, [28][29][30][31] P^P, [32][33] N^P^N [34] and SHOP-types [35] and other tridentate coordination systems. They will be introduced separately in the following.…”