Synthesis of B₂H₅FeCo(CO)₆, Fe₂Co(CO)₉(μ-CO)BH₂, FeCo₂(CO)₉(μ-CO)BH, FeCo₂(CO)₉(BH)₂, and HFe₃Co(CO)₁₂BH. Co(CO)₃Fragment Addition and Fragment Exchange in Ferraborane Clusters

Abstract

The reactions of Co2(CO)8 with the ferraboranes B2H6Fe2(CO)6, HFe3(CO)9BH4, HFe3(CO)10BH2, and HFe4(CO)12BH2 lead to fragment addition and/or fragment exchange. Thus, the new mixed-metal metallaboranes B2H5FeCo(CO)6 (1), Fe2Co(CO)9(μ-CO)BH2 (2), FeCo2(CO)9(μ-CO)BH (3), FeCo2(CO)9(BH)2 (4), and HFe3Co(CO)12BH (5) have been isolated in modest yields and characterized spectroscopically. Comparison of selected spectroscopic and chemical properties of isoelectronic pairs of hetero- and homometallaboranes defines the perturbation of the cluster network by the replacement of HFe by Co. Both direct effects due to the different metal atoms and indirect effects resulting from the differing number of skeletal hydrogen atoms are observed. Consistent with the radical mechanism suggested for Co(CO) x fragment addition to and exchange with organometallic clusters, a radical mechanism is proposed. However, the metallaborane reactions require neutral molecules and appear to be initiated by H atom transfer whereas the analogous anionic organometallic reactions proceed via electron transfer.

Reactions of the Cobaltaborane 2,4-{(η5-C5Me5)Co}2B3H7with Metal Fragments. Synthesis and Characterization ofnido-1-{(η5-C5Me5)Co}-2-{(CO)3Fe}B3H7andarachno-(η5-C5Me5)(CO)CoB3H7

“…Many of the observations concern tetrahedral M 3 E clusters, , and in at least one instance involving Co 2 (CO) 8 , the presence of a radical pathway is strongly implicated , On the other hand, although cluster degradation by Lewis bases is well-established, the effective degradation by a metal fragment, as seen in the formation of 3 , is not. Undoubtedly it takes place but may be hidden in many cases by the complexity of the systems.…”

“…Two new metallaboranes are produced in modest to good yield by metal fragment substitution in one case and metal fragment loss in the other. The former has been observed in related organometallic clusters as well as metallaborane chemistry . The latter constitutes a new route to so-called “borallyl” complexes previously prepared from [B 3 H 8 ] - and mononuclear metal complexes of Ir, , Pd, , and Pt − with phosphine ancillary ligands.…”

“…24 The latter constitutes a new route to so-called "borallyl" complexes previously prepared from [B 3 H 8 ]and mononuclear metal complexes of Ir, 25,26 Pd,27,28 and Pt 29-31 with phosphine ancillary ligands. Both compounds are characterized spectroscopically in solution and with singlecrystal X-ray diffraction in the solid state.…”

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

“…The presence of radicals in the chemistry of Co 2 (CO) 8 is well established, and several studies have implicated their presence in metal cluster chemistry . We have provided circumstantial evidence for their presence in the reactions of metallaboranes with Co 2 (CO) 8 . , Hence, it is likely that in this system the chemistry features a prominent role for the Co(CO) 4 radical. Thus, we postulate the reaction pathway given in Chart .…”

Deprotonation of Ferraborane Clusters and Their Relative Acidities

“…The Brønsted acidities of transition metal hydrides and metal carbonyl hydrides is of general interest because of their importance in a variety of preparative reactions and theoretical studies. , The relative acidities of metal carbonyl cluster hydrides and those of borane clusters , have been related to the structural arrangements and the relative sizes of the cluster cores. The only reported comparisons of Brønsted acidities in metallaborane clusters found that the Brønsted acidity of B 2 H 5 FeCo(CO) 9 is less than that of B 2 H 6 Fe 2 (CO) 9 , contrary to prediction based on the relative acidities of isoelectronic monometallic analogues. The authors concluded that the number of endo-bridging hydrogens in B 2 H 6 Fe 2 (CO) 9 must have a greater effect on the protic nature of a hydrogen atom than the more subtle change in metal identities.…”