Synthesis, Structure, and Reactivity of Mixed-Ligand Dinuclear Ruthenium Polyhydrido Complexes Supported by 1,4,7-Trimethyl-1,4,7-triazacyclononane and Bulky Phosphine Ligands

Abstract

To construct electronically and sterically anisotropic reaction sites of dinuclear cluster, mixed-ligand diruthenium pentahydrido complexes [Cn*Ru(μ-H) 3 Ru-(H) 2 (PR 3 ) 2 ] + (Cn* = 1,4,7-trimethyl-1,4,7-triazacyclononane; R = Cy (3a), i Pr (3b), cyclopentyl (Cyp, 3c)) were synthesized by the reaction of [Cn*RuH(H 2 ) 2 ] + (1) with Ru-(H) 2 (H 2 ) 2 (PR 3 ) 2 (R = Cy (2a) i Pr (2b), Cyp (2c)). The treatment of 3a−c with KH afforded the corresponding neutral tetrahydrido complexes Cn*Ru(μ-H) 3 RuH(PR 3 ) 2 (R = Cy (4a), i Pr (4b), Cyp (4c)). The structures of 3 and 4 were confirmed by X-ray diffraction studies. Introduction of the Cn* ligand into the cluster increased the electron density at the Cn*ligated metal center and significantly stimulated reactivitiy toward molecular nitrogen and carbon dioxide. Complexes 3a−c reacted with molecular nitrogen to produce the terminal dinitrogen complexes [Cn*Ru(N 2 )(μ-H) 2 RuH(PR 3 ) 2 ] + (R = Cy (5a), i Pr (5b), Cyp (5c)), which readily underwent dimerization to form the bridging dinitrogen complexes [(μ-N 2 ){RuCn*(μ-H) 2 RuH(PR 3 ) 2 } 2 ] 2+ (R = i Pr (6b), Cyp (6c)), through the liberation of N 2 . Cationic complexes 3a−c reacted with CO 2 to produce the bridging formato complexes [Cn*Ru(μη 1 :η 1 -O 2 CH)(μ-H) 2 Ru(H 2 )(PR 3 ) 2 ] + (R = Cy (7a), i Pr (7b), Cyp (7c)), whereas neutral 4a−c reacted with CO 2 to form the carbonyl complexes [Cn*Ru(CO)(μ-H) 2 RuH(PR 3 ) 2 ] + (R = Cy (9a), i Pr (9b), Cyp (9c)), via cleavage of the CO bond.

Activation of Dinitrogen by Polynuclear Metal Complexes

“…Two mixed-ligand dinuclear clusters (Cn*Ru)­(μ 2 -H) 2 (RuH­(PR 3 ) 2 ) were bridged together by a dinitrogen bridge forming [{RuCn*­(μ 2 -H) 2 RuH­(PR 3 ) 2 } 2 (μ-1,2-N 2 )]­(PF 6 ) 2 , 128-R , where Cn* = 1,4,7-trimethyl-1,4,7-triazacyclononane and R = i Pr and Cyp or cyclopentyl (Figure ). The cyclopentyl congener was structurally characterized with the observed distances of 1.135(5) Å and 1.937(3) Å for the N–N and Ru–N­(N 2 ) bonds, respectively, being comparable to other dinuclear ruthenium dinitrogen complexes.…”

“…where Cn* = 1,4,7-trimethyl-1,4,7-triazacyclononane and R = i Pr and Cyp or cyclopentyl (Figure 102). 239 The cyclopentyl congener was structurally characterized with the observed distances of 1.135(5) Å and 1.937(3) Å for the N−N and Ru− N(N 2 ) bonds, respectively, being comparable to other dinuclear ruthenium dinitrogen complexes.…”

Stabilizing hydrogen-mediated sextuple bonds by quintuple superatomic bonding and a bond

“…In addition to direct covalent bonds involving overlaps between metal orbitals, there is another well-established strategy to facilitate metal-metal multiple bonding, namely, using bridging ligands, for example, hydrogen atoms. 8,25 Various bimetallic compounds that feature bridging hydrides were synthesized and characterized, including single [M(μ-H)M], 26,27 double [M(μ-H) 2 M], 28,29 triple [M(μ-H) 3 M] [30][31][32] and quadruple [M (μ-H) 4 M] [33][34][35] (where M refers to metal) hydrogen bridges. The bonding properties of compounds that feature hydride ligands can be rationalized by a three-center two-electron (3c-2e) hydrogen bridge bond, 25,36 just like that in diborane.…”