Chemistry of Homo- and Heterometallic Bridged-Borylene Complexes

Abstract

Thermolysis of [(Cp*RuCO) 2 B 2 H 6 ] (1; Cp* = η 5 -C 5 Me 5 ) with [Ru 3 (CO) 12 ] yielded the trimetallaborane [(Cp*RuCO) 3 (μ 3 -H)BH] (2) and a number of homometallic boride clusters: [Cp * RuCO{Ru(CO) 3 } 4 B] (3 ), [ ( C p * R u ) 2 { R u 2 ( C O ) 8 } B H ] ( 4 ) , a n d [(Cp*Ru) 2 {Ru 4 (CO) 12 }BH] (5). Compound 2 is isoelectronic and isostructural with the triply bridged borylene compounds [(μ 3 -BH)(Cp*RuCO) 2 (μ-CO){Fe(CO) 3 }] (6) and [(μ 3 -BH)(Cp*RuCO) 2 (μ-H)(μ-CO){Mn(CO) 3 }] (7), where the [μ 3 -BH] moiety occupies the apical position. To test if compound 2 undergoes hydroboration reactions with alkynes, as observed with 6, we performed the reaction of 2 with the same set of alkynes under photolytic conditions. However, neither 2 nor 7 undergoes hydroboration to yield a vinyl−borylene complex. On the other hand, thermolysis of 6 with trimethylsilylethylene yielded the novel diruthenacarborane [1,1,7,7,7-(CO) 5 -2,3-(Cp*) 2 -μ-2,3-(CO)-μ 3 -1,2,3-(CO)-5-(SiMe 3 )-pileo-1,7,2,3,4,5-Fe 2 Ru 2 C 2 BH] ( 8). The solid-state X-ray diffraction results suggest that 8 exhibits a pentagonal -bipyramidal geometry with one additional CO capping one of its faces. Cluster 3 is a boride cluster where boron is in the interstitial position of a square-pyramidal geometry, whereas compound 4 can be described as a tetraruthenium boride in which the Ru 4 butterfly skeleton has an interstitial boron atom. Electronic structure calculations of compound 2 employing density functional theory (DFT) generate geometries in agreement with the structure determinations. The existence of a large HOMO−LUMO gap in 2 is in agreement with its high stability. Bonding patterns in the structure have been analyzed on the grounds of DFT calculations. Furthermore, the B3LYP-computed 11 B and 1 H chemical shifts for compound 2 precisely follow the experimentally measured values. All the compounds have been characterized by IR and 1 H, 11 B, and 13 C NMR spectroscopy, and the geometries of the structures were unambiguously established by crystallographic analyses of 2−4 and 8.

First‐Row Transition‐Metal–Diborane and –Borylene Complexes

“…However, the nature of these interactions varies 2. 8c, 33–35 Earlier, we and others synthesized various trimetallic triply bridged borylene complexes, for example, [{(η 5 ‐C 5 Me 5 )Ru} 3 (μ‐H) 3 (μ 3 ‐BX)]36 (X=H, CN, OMe, OEt), [(CpCo) 3 (μ 3 ‐BPh)(μ 3 ‐PPh)],37 [(μ 3 ‐BX){[(η 5 ‐C 5 H 4 Me)Mn(CO) 2 ][Pd‐(PCy 3 )] 2 }]38, 40 (X= t Bu, Cl; Cy=cyclohexyl), [(μ 3 ‐BH)(Cp*RuCO) 2 (μ ‐ CO){Fe(CO) 3 }],39 [(μ 3 ‐BH)‐(Cp*RuCO) 2 (μ‐H)(μ‐CO){Mn(CO) 3 }],39 [(μ 3 ‐BH)(Cp*TaCO) 2 (μ ‐ CO){Fe(CO) 3 }],39 [(Cp*Co) 2 (μ 3 ‐BH)(μ‐CO)M(CO) 5 }]29 (M=Cr, Mo, and W), [(Cp*Fe(CO)(μ‐CO)M(PCy 3 )(μ‐Br)Pt(PCy 3 )Br(μ 3 ‐B)] (M=Pd, Pt; Cy=cyclohexyl),41 and [(Cp*RuCO) 3 (μ 3 ‐H)BH]42 (Table 1, see below). As an extension of our earlier work, we set out to synthesize new species containing other metal‐carbonyl fragments.…”

“…Since the discovery of borylene complexes, the chemistry of transition‐metal complexes of boron has attracted significant attention in terms of structure, bonding,8 and reactivity 33. 42, 49–51 We have recently reported the synthesis of several trimetallic triply bridged borylene compounds, one of which has been successfully utilized in the formation of a vinyl borylene complex. However, homotrimetallic borylene complexes of first‐row transition metals are very rare because they are highly air‐ and moisture‐sensitive.…”

η4‐HBCC‐σ,π‐Borataallyl Complexes of Ruthenium Comprising an Agostic Interaction

“…Althought he interatomic distance between the Ru ande thylenic carbon atoms in 5-7 are well within the sum of the van der Waals radii of the two atoms, the RuÀBd istance (average 2.355 ) is found to be slightly elongated. [31] The terminal olefinic carbon in 5 and 7 approacht he ruthenium more closely than 6,r esulting longerR u ÀCd istance in 6 (2.283 (2) ). The C= Cb ond distancesi n5-7 (1.403(4)for 5,1 .396(3) f or 6,a nd 1.410(4) f or 7)a re comparable to that of the cationic olefin complex[ ( h 5 -C 5 Me 5 )Fe(CO) 2 -H 2 C=CHtBu] + ,( 1.393 (9) ).…”

Neutral heterometallic cluster containing ketenylidene ligand: [Cp*Mo(CO) 2 ( μ -H)Ru 2 (CO) 6 ( μ 3 - ɳ 1 -CCO)] (Cp* = ɳ 5 -C 5 Me 5 )

“…The metallaborane chemistry is mainly dominated by boron-rich rather than metal-rich compounds [Ru 3 (CO) 12 ] at higher temperature [28]. As shown in Scheme 1, thermolysis of arachno-1 with [Ru 3 (CO) 12 ] also yielded heterometallic boride cluster 3 in 16% yield.…”

“…The boron atom is lying 0.305 Å below the square face made of Mo1-Ru1-Ru2-Ru4, which is 0.07 Å shorter than the homometallic boride cluster [Cp*RuCO{Ru(CO) 3 } 4 B] [28]. This molecule is isoelectronic and isostructural with other M 5 B frameworks, for example, [Cp*RuCO{Ru(CO) 3 } 4 B] [28] and [Ru 5 (CO) 15 B{AuPPh 3 }] [29]. Thus, cluster 3 can be viewed as nido-square pyramidal with boron in the semi-interstitial position.…”