Synthesis, Structure, and Bonding of Bimetallic Bridging Borylene and Boryl Complexes

A new
synthetic route for the synthesis of diruthenium boryl complexes
has been established. Thermolysis of an arachno-ruthenaborane,
[(Cp*Ru)2B3H8(CS2H)] (1; Cp* = η5-C5Me5),
with phenylacetylene led to the formation of the bridging boryl borylene
complex [(Cp*Ru)2(μ-HBS2CH2-κ2B:κ2S)­{μ-B­(C6H4)­C­(CH3)-κ2B:κ2C}] (2). In parallel to the formation of 2, the reaction also yielded [(Cp*Ru)­(μ-H)­BH­{HCC­(H)­Ph}­{SC­(H)­S}]
(3a) and [(Cp*Ru)­(μ-H)­BH­(PhCCH2)­{SC­(H)­S}] (3b). To understand the reaction pathways
for the formation of 2, we have thermolyzed 1 in toluene, which afforded the ruthenium bridging bis­(boryl) complex
[(Cp*Ru)2(μ-HBS2CH2-κ2B:κ2S)­{μ,η2:η2-SBH}] (4) along with the nido-ruthenathiaborane [(Cp*Ru)2(Me)­(S2B2H3)] (5). nido-5 is structurally and electronically similar to nido-[(Cp+Ru)2(S2C2Ph2)] (Cp+ = η5-C5Me4Et), which can be generated from the room-temperature
reaction of [(Cp+Ru)2(μ,η1:η1-S2)­(μ,η2:η2-S2)] with diphenylacetylene. Thus, nido-5 can be defined as a true mimic of the organometallic
cluster nido-[(Cp+Ru)2(S2C2Ph2)]. The complex [(Cp*Ru)2(μ,η1:η1-S2)­(μ,η2:η2-S2)] (6), the
Cp* analogue of [(Cp+Ru)2(μ,η1:η1-S2)­(μ,η2:η2-S2)], can be isolated from the reaction
of Li­[BH2S3] with [Cp*RuCl2]2 along with the diruthenium boryl complex [(Cp*Ru)2(μ,η1:η1-S2)­(μ-S2BH-κ1B:κ2S:κ2S′)]
(7), in which the boryl unit (S2BH) possesses
no bulky heterocyclic ligand. Theoretical studies were performed to
shed light on the bonding of these borylene and boryl complexes. The
theoretical calculations reveal that the stability of these complexes
is due to the strong interaction between the borylene and boryl units
and the ruthenium centers.