Coordination and Hydroboration of Ru(II)‐Borate Complexes: Dihydridoborate vs. Bis(dihydridoborate)

Abstract

Treatment of [Cp*RuCl2]2, 1, [(COD)IrCl]2, 2 or [(p‐cymene)RuCl2]2, 3 (Cp*=η5‐C5Me5, COD= 1,5‐cyclooctadiene and p‐cymene=η6‐iPrC6H4Me) with heterocyclic borate ligands [Na[(H3B)L], L1 and L2 (L1: L=amt, L2: L=mp; amt=2‐amino‐5‐mercapto‐1,3,4‐thiadiazole, mp=2‐mercaptopyridine) led to the formation of borate complexes having uncommon coordination. For example, complexes 1 and 2 on reaction with L1 and L2 afforded dihydridoborate species [LAM(μ‐H)2BHL] 4–6 (4: LA=Cp*, M=Ru, L=amt; 5: LA=Cp*, M=Ru, L=mp; 6: LA=COD, M=Ir, L=mp). On the other hand, treatment of 3 with L2 yielded cis‐ and trans‐bis(dihydridoborate) species, [Ru{(μ‐H)2BH(mp)}2], cis‐7 and trans‐7. The isolation and structural characterization of fac‐ and mer‐[Ru{(μ‐H)2BH(mp)}{(μ‐H)BH(mp)2}], 8 from the same reaction offered an insight into the behaviour of these dihydridoborate species in solution. Fascinatingly, despite having reduced natural charges on Ru centres both at cis‐and trans‐7, they underwent hydroboration reaction with alkynes that yielded both Markovnikov and anti‐Markovnikov addition products, 10 a–d.

Synthesis and Chemistry of Dihydridoborate Group 7 Metal Complexes with Varied N,E-Chelated Ligands (E = O, NH, or S)

“…As shown in Figure , the solid-state X-ray structure of 8 shows monohydroborated bis­(σ)­borated species, formed via Markovnikov addition. Also, it is plausible to assume that the formation of 8 is through trans -hydroboration of alkynes, similar to that reported by Miyaura and us. ,, The Mn–B distance of 2.152(8) Å is comparable to that of its precursor 5 (2.148(3) Å) and other Mn-dihydridoborated species. ,, The olefinic moiety in 8 resides away from the {MnBH 2 } plane. The olefinic C23–C24 bond length of 1.317(8) Å is comparatively shorter as compared to the typical CC bond distance.…”

“…2-mercaptopyridine, 2-amino-5-mercapto-1,3,4-thiadiazole, 2-hydroxypyridine, 2-aminopyridine, 2,6-diaminopyridine, [NaBH 4 ], [Mn 2 (CO) 10 ], [Re 2 (CO) 10 ], and phenyl acetylene were purchased commercially (Sigma-Aldrich) and utilized as they were given. Following the procedures outlined in the literature, compounds like Na­[(H 3 B)­mp], Na­[(H 3 B)­amt], and the external reference for 11 B NMR, [Bu 4 N]­[B 3 H 8 ], were synthesized. Silica gel TLC plates (250 μm aluminum supported) were used for thin layer chromatography.…”

“…In the course of our continuous work to isolate borate complexes, lately, we have isolated a number of dihydridoborate complexes from the reactions of Na­[H 3 B­(mp)] with [Cp*RuCl 2 ] 2 , [(COD)­IrCl] 2 , and [( p -cymene)­RuCl 2 ] 2 , which upon reaction with alkynes produced hydroborated products . Herein, in this article, we report the synthesis, structures, and chemistry of various dihydridoborate metal complexes comprised of both soft (sulfur) and hard (nitrogen and oxygen) donor atoms coordinated to metal (Figure ).…”

The transition metal-catalysed hydroboration reaction

“…73 Since its development, this protocol has seen some use in synthetic chemistry. 73,[349][350][351][352][353][354] Ruthenium, 268,309,355,356 copper, 357 cobalt, 358,359 and iron 360,361 catalysts have since also been shown to be capable of the same transformation. It should be noted that in many cases, the reaction proceeds through initial migration of the alkynyl proton (see Section 2.3 trans-Hydroboration of alkynes).…”

Three-Center M–H–B Bonds Are Strong Field Interactions. Synthesis and Characterization of M(CH2NMe2BH3)3 Complexes of Titanium, Chromium, and Cobalt

“…Essentially, all known late transition metal borohydride compounds contain ancillary ligands (especially carbon monoxide, phosphines, and olefins) that stabilize the metals with respect to reduction to the zerovalent state. Among these late transition metal borohydride compounds are some in which the borohydride groups are incorporated into chelating ligands of the type L-BH 3 (often, L is attached to the borohydride unit by means of some intervening atoms), where L is a Lewis base such as a phosphine, – chalcogen, – carbene, pyrazole, , or amide group …”