Synthesis of mono- and ditungstaboranes from reaction of Cp*WCl4 and [Cp*WCl2](2) with BH3 center dot thf or LiBH4 (Cp* = eta(5)-C5Me5). Control of reaction pathway by choice of monoboron reagent and oxidation state of metal center

Journal article

Reaction between Cp*WCl4 or [Cp*WCl2]2 (Cp*= η5·C5Me5) and BH3·thf affords the new tungstaborane (Cp*WCl)2B2H6, 2, which reacts with further BH3·thf to give (Cp*W)2B5H9, 1. The structure of 1 has been determined by a single-crystal X-ray diffraction study and is best described as a bicapped trigonal bipyramidal, the same as previously found for Cr and Mo analogues. The first step of this reaction is reduction of Cp*WCl4 to [Cp*WCl2]2 by BH3· thf, paralleling that of the Cp*MoCl4 system. In contrast with its lighter congener, reaction between LiBH4 and Cp*WCl4 or [Cp*WCl2]2 gives different metallaboranes depending on the oxidation state of the starting material and rate of addition of borane. With Cp*WCl4 and fast addition of LiBH4 the monometallic, crystallographically characterized, metallaborane nido-2-(Cp*WH3)B4H8, 3, is formed in good yield along with the coproduct (Cp*WH3)2B2H6, 4. We have observed the time-dependent behavior of the formation of 3, allowing the elucidation of intermediates on the reaction pathway. Reaction between [Cp*WCl2]2 and 6 equiv of LiBH4 affords only (Cp*W)2(B2H6)2, 5, demonstrating that in the formation of 3 and 4 LiBH4 does not prereduce Cp*WCl4 to [Cp*WCl2]2. Slow addition of LiBH4 to Cp*WCl4 results in the reduced, dimeric complex (Cp*W)2HCl(B2H6), 6, which is formulated as having a W≡W triple bond. © 1999 American Chemical Society.

Authors: Weller, A; Shang, M; Fehlner, T

• Publication status: Published
• Journal: ORGANOMETALLICS
• Volume: 18
• Issue: 1
• Pages: 53-64
• Publication date: 1999-01-04
• DOI: 10.1021/om980743h
• EISSN: 1520-6041
• ISSN: 0276-7333
• Language: English