A Capped Octahedral MHC₆ Compound of a Platinum Group Metal

Abstract

A MHC6 complex of a platinum group metal with a capped octahedral arrangement of donor atoms around the metal center has been characterized. This osmium compound OsH{κ(2) -C,C-(PhBIm-C6 H4 )}3 , which reacts with HBF4 to afford the 14 e(-) species [Os{κ(2) -C,C-(PhBIm-C6 H4 )}(Ph2 BIm)2 ]BF4 stabilized by two agostic interactions, has been obtained by reaction of OsH6 (PiPr3 )2 with N,N'-diphenylbenzimidazolium chloride ([Ph2 BImH]Cl) in the presence of NEt3 . Its formation takes place through the C,C,C-pincer compound OsH2 {κ(3) -C,C,C-(C6 H4 -BIm-C6 H4 )}(PiPr3 )2 , the dihydrogen derivative OsCl{κ(2) -C,C-(PhBIm-C6 H4 )}(η(2) -H2 )(PiPr3 )2 , and the five-coordinate osmium(II) species OsCl{κ(2) -C,C-(PhBIm-C6 H4 )}(PiPr3 )2 .

Preparation of Capped Octahedral OsHC6 Complexes by Sequential Carbon-Directed C–H Bond Activation Reactions

“…The Os-C(1) and Os-C(10) bond lengths of 1.997 3and 2.053(3) Å, respectively, compare well with the Os-C(chelate) distances in 4. The Os-N separations are consistent with the different trans-influence of the respective trans donor groups, decreasing in the sequence 2.109 3 (6) and , N trans to CH3CN). In agreemet with 4, the 13 C{ 1 H} NMR spectra of 8 and 9, in acetonitrile-d3, at room temperature show singlets at about 186 (NHC) ppm and between 136 and 149 (Ph) ppm due to the metalated carbon atoms of the C,C-chelate ligand.…”

“…Then, we decided to substitute the chloride ligand by a better leaving group as the triflate anion (OTf). The treatment of 4 and 5 with the stoichiometric amounts of AgOTf, in dichloromethane, at room temperature produces the precipitation of AgCl and the formation of the triflate derivatives Os(OTf){κ 2 -C,C-(MeL-C6H4)}(η 6 -pcymene) (L = BIm (6), BIm * (7)), which were isolated as green solids in 80% (6) and 94% (7) yield (Scheme 3). In accordance with 4 and 5, the 13 C{ 1 H} NMR spectra of 6 and 7, in dichloromethane-d2, at room temperature contain singlets at about 182 and 149 ppm, due to the metalated carbon atoms of the benzimidazolylidene core and the phenyl substituent, respectively.…”

“…Figure 2 shows a view of the cation of the salt. The coordination geometry around the osmium atom can be rationalized as a distorted octahedron with N(3)-Os-N (6), N(4)-Os-C(1), and N(5)-Os-C(10) angles of 175.71(10)º, 171.89(11)º and 178.05(10)º, respectively. The Os-C(1) and Os-C(10) bond lengths of 1.997 3and 2.053(3) Å, respectively, compare well with the Os-C(chelate) distances in 4.…”

“…This disposition allows the interaction between its s orbital and the formally vacant p orbitals of the carbene carbon atoms. 6 In agreement with the symmetry of the molecule, the three Os-BIm bond lengths of 2.032(3) (Os-C(1)), 2.040 3(Os-C(15)), and 2.045 3 3, C(1)-Os-C(10) = 75.52 (11), C(15)-Os-C(24) = 75.71 (12), C(29)-Os-C(38) = 75.27 (11).…”

Assembly of a Dihydrideborate and Two Aryl Nitriles to Form a C,N,N′-Pincer Ligand Coordinated to Osmium

“…The pincer ligands coordinated to this element mainly involve neutral 10 or monoanionic 10f,11 moieties, which result from the simple coordination of tridentate molecules 10 or the coordination of bidentate groups along with the σ-bond activation of one of their substituents, 11 whereas osmium complexes bearing dianionic pincer ligands are very rare. Examples include C,C',N-donors, which are generated by coordination of a 2e-donor N atom and two σ-bond activations at the molecule skeleton, 12 or O,N,O-, 13 C,C',C-, 14 and C,N,C-donors, 15 which are formed as a consequence of the coordination of a 2e-donor atom and a σ-bond activation at two substituents of the molecular core. [13][14][15] This paper describes the discovery of a new class of formally dianionic pincer ligands coordinated to osmium, aryl-diimineborate (C,N,N´), which are furthermore generated on the metal coordination sphere by a novel procedure involving the coupling of a coordinated dihydrideborate anion with two aryl nitrile molecules and the activation of an ortho-CH bond of the aryl group of one of them.…”