Bis(diphenylphosphino)methane-phosphonate ligands and their Pd(II), Ni(II) and Cu(I) complexes. Catalytic oligomerization of ethylene.
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.
Hamada
Adel
A
Laboratoire de Chimie de Coordination, Institut de Chimie (UMR 7177 CNRS), Université Louis Pasteur, 4 rue Blaise Pascal, F-67070 Strasbourg Cedex, France.
Braunstein
Pierre
P