Metallaborane Reactivity. Complexities of Cobalt Carbonyl Fragment Addition to 1,2-{Cp*RuH}₂B₃H₇, Cp* = η⁵-C₅Me₅, and Characterization of a Diruthenium Analogue of Pentaborane(11) 1,2-{Cp*Ru}₂(CO)₂B₃H₇

Abstract

The reaction of 1,2-{Cp*RuH} 2 B 3 H 7 (1), Cp* ) η 5 -C 5 Me 5 , with Co 2 (CO) 8 in hexane yields two major ruthenaborane products, nido-1,2-{Cp*RuH} 2 -3-Co(CO) 4 B 3 H 4 (2) and arachno-{Cp*RuH}(CO)B 3 H 7 (3), as well as two other ruthenaboranes in low yield. In toluene, benzene, and THF one of these minor ruthenaborane products is found with an enhanced yield intermediate between those of 2 and 3. This compound has been isolated and characterized in solution and the solid state as the 8 skeletal electron pair (sep) arachno 1,2-{Cp*Ru} 2 (CO) 2 B 3 H 7 (4) and shown to convert into a second isomeric form of similar stability. One isomer constitutes a diruthenium analogue of 8-sep pentaborane(11), whereas the other mimics the geometry of a known metal cluster with 8 sep. The variation in product concentrations in benzene, including [Cp*Ru(CO) 2 ] 2 , {Cp*Ru(CO) 2 }Co(CO) 4 , and HCo(CO) 4 , as a function of time and Co 2 (CO) 8 /1 ratio has been determined by 1 H and 11 B NMR spectroscopy and interpreted in terms of a reaction pathway featuring competitive Co(CO) 4 radical addition to ruthenium to yield 2 plus 3 and to boron to yield 4. The apparent solvent dependence of product distribution is attributed to impurity-initiated decomposition of the boron-based radical in hexane.

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“…In general, the monometal–carbonyl species [M(CO) 3 (CH 3 CN) 3 ] (M=Cr, Mo) are known to add metal–carbonyl fragments both in organometallic35 and metallaborane chemistry;36 however, compound 1 reacts in a surprisingly different fashion to yield 2 , which presumably results from the cluster degradation followed by carbonylation at the metal centers (Scheme ). This new diruthenatetraborane has been isolated in good yield, which provides an interesting alternative to conventional methods of carbonylation37 using monometal–carbonyl fragments. No reaction of 1 was observed with [W(CO) 3 (CH 3 CN) 3 ], and all our attempts to generate 2 from [(η 6 ‐arene)Cr(CO) 3 ] failed (Table 1).…”

Reaction of the Transition Metal Hydrides [Cp*MH2]2 (Cp* = η5-C5Me5; M = Fe, Ru) with BH3·THF to Yield Metallaboranes. Improved Kinetic Control Leads to Novel Ferraboranes

“…The reaction of open metal clusters with Co 2 (CO) 8 constitutes a useful way of generating derivatives that are often more stable than the original cluster . This approach has been useful in metallaborane chemistry as well, where metal fragment addition, metal fragment replacement, and simple CO addition to the Cp*M center have been observed. − Thus, the reaction of 3 with Co 2 (CO) 8 was examined with expectations of producing a derivative that could be structurally characterized in the solid state.…”

“…32 This approach has been useful in metallaborane chemistry as well, where metal fragment addition, metal fragment replacement, and simple CO addition to the Cp*M center have been observed. [33][34][35][36] Thus, the reaction of 3 with Co 2 (CO) 8 was examined with expectations of producing a derivative that could be structurally characterized in the solid state.…”

21 Organometallic chemistry of bi- and poly-nuclear complexes

“…while in hexanes, the mixed metal species [{Cp*Ru(CO) 2 }Co(CO) 4 ] is the major product. 88 The water soluble, electron deficient cluster [Ru 4 (µ 3 -H) 4 (η 6 -C 6 H 4 ) 4 ] 2ϩ undergoes addition reactions with nucleophiles in aqueous media to give cationic clusters, the chloride salts of which are soluble in organic solvents as well as in water.…”