Ortho-metallation reactions of 2-substituted pyridines, 1,2-, 1,3-, and 1,4-diazines, and 2,2′-bipyridyl with triosmium clusters. Crystal and molecular structure of nonacarbonyl-µ-(2,2′-bipyridyl-6-yl)-µ-hydrido-triangulo-triosmium(3Os–Os)

Abstract

2-Methyl-or 2-benzyl-pyridine, and 1,2-, 1,3-, and 1,4-diazines all react like pyridine itself with [Os,(CO),,-(C8H14)2] (CBH14 = cyclo-octene) to give complexes of the type [0s3H(CO),,(p-L)] where L is a 2-metallated heterocycle. The H n.m.r. spectrum of the 2-benzylpyridine complex shows that p-L is in a locked configuration on the n.m.r. time-scale and does not alternate its bonding between the two 0 s atoms it bridges. 2,2'-Bipyridyl reacts with [OS~(CO)~ 2] to give the related red complex [Os3H (CO)9(C10H7N2)] which contains the chelating bridging 6-metallated bipy ligand as established by a single-crystal X-ray structure determination. The crystals are monoclinic, space group P2,/c, with a = 9.113( 2), b = 13.157(2), c = 18.209(2) A, p = 91.59(2)", and Z = 4. The structure was refined to R = 0.0427 for 3 550 observed reflections. The structure of [Os,H(CO)?-(C10H7N2)] is rather like those of compounds [OS,H(CO)~~X] and in particular where X = 2-pyridyl except that in the nonacarbonyl complex described here the ortho-metallated pyridine ring is part of a 2,2'-bipyridyl chelating ligand.

Competition studies on the activation of the C_H bond of diazines by the unsaturated triangular cluster anion [Re3(μ-H)4(CO)10]−

“…Table 1). Moreover, the aromatic resonances are almost identical to those reported for the orthometallated 1,2-diazine moiety in Os 3 ( -H)( -2 -N 2 C 4 H 3 )(CO) 10 [17].…”

“…As observed in the case of the above Os cluster [17], the thermal conversion of 3 into 4 was not a selective process and at long times extensive decomposition took place, hampering the complete conversion of 3 or the possible attainment of an equilibrium ratio.…”

“…However, it was possible to obtain the orthometallated isomer of 3, namely [Re 3 ( -H) 3 ( -2 -N 2 C 4 H 3 )-(CO) 10 ] − (4), by using the thermal activation method described by Deeming et al [17]. Table 1).…”

“…It is known in fact that stable organometallic compounds can provide good models of the reactive intermediates in both homogeneous and heterogeneous catalytic processes. A particular interest is devoted to systems able to activate C-H bonds of organic ligands co-ordinated on metal clusters and several examples of these complexes have been described [5][6][7][8][9][10][11][12][13][14][15][16][17][18]. 2 …”

Two isomeric products [Os3(μ-H)(C14H9N4)(CO)9] formed by orthometallation of the cluster [Os3(C14H10N4)(CO)10] containing the chelating ligand 2,3-bis(2-pyridyl)pyrazine

“…Thermolysis of these compounds gives [Os 3 (l-H)(C 5 H 3 N-2-CH@N-iPr)(CO) 9 ] and [Os 2 (CO) 6 (R-Pyca)], with ligands donating 5 and 6 electrons, respectively [5]. The triosmium cluster [Os 3 (CO) 12 ] reacts at high temperatures [6] and more reactive ones like [Os 3 (CO) 10 L 2 ] (L = cyclooctene [7,8] or CH 3 CN [8]) react at room temperature with pyridine by orthometallation to give the l-2-pyridyl cluster [Os 3 H(l-2-C 5 H 4 N)(CO) 10 [7], which contains the chelating/bridging orthometallated bipy ligand. The interaction of 2,3-bis(2-pyridyl)pyrazine with the labile compound [Re 2 (CO) 8 (CH 3 CN) 2 ] [9] gives the complexes [Re 2 (C 14 H 10 N 4 )(CO) 8 ] and [Re 2 (CO) 8 (l-C 14 H 10 N 4 )Re 2 -(CO) 8 ], this latter compound contains the 2,3-bis(2-pyridyl)pyrazine ligand r,r-N,N-coordinated to each dinuclear rhenium group.…”