Stabilization of Classical [B₂H₅]⁻: Structure and Bonding of [(Cp*Ta)₂(B₂H₅)(μ‐H)L₂] (Cp*=η⁵‐C₅Me₅; L=SCH₂S)

Abstract

The room‐temperature reaction of [Cp*TaCl4] with LiBH4⋅THF followed by addition of S2CPPh3 results in pentahydridodiborate species [(Cp*Ta)2(μ,η2:η2‐B2H5)(μ‐H)(κ2,μ‐S2CH2)2] (1), a classical [B2H5]− ion stabilized by the binuclear tantalum template. Theoretical studies and bonding analysis established that the unusual stability of [B2H5]− in 1 is mainly due to the stabilization of sp2‐B center by electron donation from tantalum. Reactions to replace the hydrogens attached to the diborane moiety in 1 with a 2 e {M(CO)4} fragment (M=Mo or W) resulted in simple adducts, [{(Cp*Ta)(CH2S2)}2(B2H5)(H){M(CO)3}] (6: M=Mo and 7: M=W), that retained the diborane(5) unit.

Strong Be–Be bonds in double-aromatic bridged Be2(μ-SO) molecules

“…The (HCNMe) 2 BBe–BeB(HCNMe) 2 complex is another example of covalent bond formation between two Be atoms through adding radical ligands. 9 The DFT study on the mentioned complex indicates that because of excitation in the Be 2 moiety, adding two (HCNMe) 2 B ligands to this moiety can lead to the formation of a single Be–Be covalent bond. In addition, a series of complexes with strong Be–Be bonds formed by using C n H n ( n = 3, 5, 7) π-radicals were investigated.…”

Syntheses, Structures, and Electronic Properties of Mono‐ and Bimetallic Thiolato Complexes Containing Unusual Coordination Modes of Thiolato Ligands

“…The Ta1‐S1 bond length of 2.5321(11) Å is elongated whereas, the Ta1‐S2 got reduced (2.5342(11) Å) as compared to the Ta−S bond distances in 5 (Ta1−S5 2.4532(16) Å and Ta1‐S3 2.6205(16) Å). The average Mo−S bond length of 2.5281 Å is comparable with that of Mo−S bonds in [{(Cp*Ta)(CH 2 S 2 )} 2 (B 2 H 5 )(H){Mo(CO) 3 }] [30] (2.542(9) Å and 2.565 (9) Å). However, this is significantly longer as observed in complexes, [CpMoSC 2 H 4 S] 2 [22] (2.352(2)–2.479(2) Å) and [Mn 3 (CO) 6 (SCH 2 CH 2 CH 2 S) 3 ] [15a] (2.3111(9)–2.3975(9) Å).…”

“…The oxidation state of tantalum remained unaffected (+5), whereas the oxidation state of molybdenum stayed zero. The Ta1−Mo2 bond length in 6 of 2.9455(4) Å is significantly shorter as compared to the Ta−Mo bond distance in [{(Cp*Ta)(CH 2 S 2 )} 2 (B 2 H 5 )(H){Mo(CO) 3 }] [30] (3.245(3) Å). The molybdenum tricarbonyl fragment is coordinated to the tantalum thiolato part through three sulfur atoms and the corresponding Ta−S bond length ( avg .…”

Diborane and Triborane Species in the Coordination Sphere of Group-8 Transition Metals

“…Recently, we have isolated and structurally characterized dithiolate-based classical [B 2 H 5 ] − diborane species [(Cp*Ta) 2 (μ,η 2 :η 2 -B 2 H 5 )(μ-H)(κ 2 ,μ-S 2 CH 2 ) 2 ] from the reaction of [Cp*TaCl 4 ] with [LiBH 4 ·THF] followed by addition of [S 2 C·PPh 3 ] in excess . Thus, the investigation of CS 2 -derived borate ligands with early and late transition-metal precursors became of interest.…”

“…Further, as shown in Scheme S1, the calculated positive ΔG (change in free energy) of the possible reaction pathways, nido-4 to arachno-5 and arachno-5 to nido-6, support the requirements of additional energy for the formation of arachno-5 (+ 11.8107 kJ/mol) and nido-6 (+9.0150 kJ/mol), respectively, whereas the ΔG for the formation of hypothetical nido-4′ from nido-4 is notably positive (+51.9466 kJ/mol) as compared to arachno-5. 39 Thus, the investigation of CS 2 -derived borate ligands with early and late transition-metal precursors became of interest. With an objective to extend a similar methodology for the isolation of structurally exciting thiolate-stabilized diborane species of late transition metals in a similar approach, we carried out the photolytic reaction of arachno-5 with an in situ generated intermediate from the reaction of CS 2 and [LiBH 4 •THF] for 4 h in THF.…”