Synthesis and Characterization of Osmium(II) Trispyrazolylborate Complexes

Abstract

Treatment of H2OsBr6 with excess 1,5-cyclooctadiene (cod) in boiling tert-butyl alcohol affords the polymer [OsBr2(cod)]x (1), which reacts with acetonitrile to form the mononuclear adduct OsBr2(cod)(CH3CN)2 (2). Polymer 1 reacts with potassium trispyrazolylborate (KTp) in ethanol to afford the hydride TpOs(cod)H (3) and the bromide complex TpOs(cod)Br (4). Bromide complex 4 reacts with sodium methoxide in methanol to afford TpOs(cod)OMe (5), which has been structurally characterized. Treatment of hydride 3 with methyl trifluoromethanesulfonate (MeOTf) in diethyl ether results in loss of methane and formation of the triflate complex TpOs(cod)OTf (6), which reacts with MgMe2 to give the methyl complex TpOs(cod)Me (7). The addition of bis(dimethylphosphino)methane (dmpm) to the known compound TpOs(PPh3)2Cl yields a mixture of the substitution products TpOs(eta1-dmpm)(PPh3)Cl (8) and TpOs(eta2-dmpm)Cl (9); the latter reacts with methyllithium to generate the methyl compound TpOs(dmpm)Me (10). NMR and IR data for these new compounds are reported. Crystal data for 5.MeOH at -80 degrees C are as follows: monoclinic, P2(1)/n, a = 10.728(1) A, b = 14.004(2) A, c = 13.906(2) A, beta = 102.42(6) degrees , V = 2040.3(5) A3, Z = 4, R(F) = 0.0247 for I > or = 2sigma(I), and R(wF2) = 0.0539 for all data.

Dichlorido(η4-cycloocta-1,5-diene)bis(triphenylphosphine)osmium(II)

“…As shown in Fig.1 (Esteruelas et al, 2006) and TpOs(η 4 -COD)OMe (Tp = trispyrazolylborate) (2.141-2.198 Å) (Dickinson & Girolami, 2006). The C(1)-C(2) (1.403 (6) Å) bond length is significntly longer than a free olefinic double bond (≈ 1.34 Å) (Orpen et al, 1989) and is typical for a coordinated C═C double bond, which is also close to the C═C bond lengths found in [H(EtOH) 2 [{OsCl(η 4 -COD)} 2 (µ-H)(µ-Cl) 2 ] (1.393-1.422 Å) and TpOs(η 4 -COD)OMe (1.396 (5) and 1.399 (5) Å).…”

“…For general background to Ru II and Os II COD complexes, see: Bennett & Wilkinson (1959); Albers et al (1989); Cucullu et al (1999); Coalter & Caulton (2001); Alvarez et al (2001); Winkhaus et al (1966); Schrock et al (1974); Dickinson & Girolami (2006). For C C bond lengths for free olefinic double bonds, see: Orpen et al (1989).…”

“…For C C bond lengths for free olefinic double bonds, see: Orpen et al (1989). For related CODcoordinated Os II complexes, see: Esteruelas et al (2006); Dickinson & Girolami (2006).…”

“…Although the analogous osmium polymer [OsCl 2 (COD)] x is also known, its utility as a starting material has remained relatively unexplored partially due to the difficuly in its preparation (Winkhaus et al, 1966;Schrock et al, 1974;Dickinson & Girolami, 2006). In our search for other potential precusors for the synthesis of osmium compounds, we have prepared [OsCl 2 (η 4 -COD)(PPh 3 ) 2 ] readily from the reaction of OsCl 2 (PPh 3 ) 3 with COD.…”

Syntheses, structures and electrochemical properties of homoleptic ruthenium(III) and osmium(III) complexes bearing two tris(carbene)borate ligands

“…It is surprising that no ruthenium and osmium complex with the Ph[B(R-ImH) 3 ] ligand has been reported yet. In comparison, the chemistry of Ru and Os complexes with tris(pyrazolyl)borate (Tp) ligand (C, Chart 1) has been extensively studied [27][28][29][30][31][32][33][34].Herein we report the synthesis, structure, X-ray photoelectronic spectroscopy (XPS), and electrochemical properties of ruthenium(III) and osmium(III) complexes [PhB(ImMe) 3 ] 2 M(OTf) (M = Ru, 1a; M = Os, 1b) with two tris(carbene)borate ligands. To our knowledge, 1b is the first Os(III)-NHC complex and 1a is among a limited number of Ru(III)-NHC complexes reported in the literature [35].…”