Synthesis and Reactivity of Semibridging Borylene Complexes

Abstract

Reaction of the terminal borylene complexes [(OC)5MBN(SiMe3)2] (M = Cr, W) with [M‘(PCy3)] (M‘ = Pd, Pt) at room temperature led to spontaneous formation of the heterodinuclear complexes [(OC)4M(μ-CO){μ-BN(SiMe3)2}M‘(PCy3)2] (M = Cr, M‘ = Pd; M = W, M‘ = Pd; M = Cr, M‘ = Pt) with concomitant liberation of PCy3. X-ray diffraction studies revealed that the borylene ligand adopts a semibridging position between the two different metal centers, thus establishing a new coordination mode for borylenes and providing further experimental evidence for the theoretically predicted close relationship between BR and CO. After prolonged reaction times the liberated phosphine substitutes the carbonyl group in trans-position to the borylene moiety, forming complexes of the type [(Cy3P)(OC)3M(μ-CO){μ-BN(SiMe3)2}M‘(PCy3)] (M = Cr, M‘ = Pt; M = W, M‘ = Pt; M = W, M‘ = Pd). Heating or photolytic activation of [(OC)4M(μ-CO){μ-BN(SiMe3)2}Pd(PCy3)] afforded the terminal borylene complexes trans-[(Cy3P)(OC)4MBN(SiMe3)2], which were fully characterized in the case of M = Cr. Structural data of trans-[(Cy3P)(OC)4CrBN(SiMe3)2] confirm the presence of an enhanced Cr−B π-back-donation imposed by the phosphine ligand in trans-position.

Late‐Transition‐Metal Complexes as Tunable Lewis Bases

“…[34][35][36] Similarly, Bourissou et al have successfully employed bi-and tridentate phosphanes for the synthesis of supported metal-base adducts of Group 13 elements, [37][38][39][40][41][42][43] and we disclosed the pronounced propensity of electron-rich metal fragments of the type [M-A C H T U N G T R E N N U N G (PR 3 )] (M = Pd, Pt) to form dative bonds to metal-coordinated boryl and borylene ligands. [44][45][46][47][48][49][50][51][52] The latter species without exception display CO bridges between the metal centers and thus again supported dative metal-element bonds. Neutral Lewis pairs of the type…”

Monohaloboryls (BHX−) as Bridging Ligands: Observable Dinuclear σ‐(Halo)boranyl Intermediates in the Synthesis of Metalloborylenes

“…1.996(6) for [(OC) 5 Cr=B=NA C H T U N G T R E N N U N G (SiMe 3 ) 2 ]). [12,16] The corresponding rhenium-boryl compounds were synthesized by a similar synthetic route: BX 3 (X = Cl, Br) was added to an excess of [Re(CO) 5 ]Na in either toluene or n-hexane (Scheme 2), upon which the reaction mixtures immediately turned orange. After removal of all of the volatile compounds in vacuo and extraction of the yellow solid with n-hexane (20 mL), the dichloroboryl complex (4) was obtained as an analytically pure colorless solid in 77 % yield after sublimation, whereas the thermally less-stable dibromoboryl species (5) was obtained as a light-yellow solid in 37 % yield by crystallization from n-hexane at À30 8C.…”

A Bromide‐bridged Platinum(II) Complex as Precursor to a Neutral Platinum Compound with a Base‐Stabilized Borylene Ligand

“…Boryl and borylene complexes of transition metals are a topic of constant research activity because of the important role especially the former play as intermediates for transition metal‐catalyzed functionalization (hydro‐ 1–4 and diboration 5,6) of organic substrates. Through the oxidative addition of B–Hal bonds 7,8 to the electron rich platinum(0) compound [Pt(PCy 3 ) 2 ] we were able to isolate a variety of boryl complexes of the type trans ‐[(Cy 3 P) 2 Pt(Hal){B(R)R’}] (Hal = Br, R = Br, R’ = Fc ( 3 ), Mes, t Bu, NMe 2 , Pip, Br; R = R’ = NMe 2 , RR’ = Cat, Cat–4‐ t Bu; Hal = R = Cl, R’ = NMe 2 , Mes, t Bu, Mes = mesityl, Pip = piperidyl, Cat = catecholato) 9–11. Most of these compounds can be converted to T‐shaped cationic species, of which the Fc‐substituted compound ( 4 ) was the first to be structurally characterized 12–14.…”