Reactivity of [(C₅Me₅)Fe(C₅H₄BBr₂)] and [(OC)₃Mn(C₅H₄BBr₂)] toward Et₃SiH: Facile Access to [(OC)₃Mn(C₅H₄BH₂)]₂ and to Boron-Bridged Dinuclear Organometallics

Abstract

The reaction of Fc # BBr 2 with 2 equiv of Et 3 SiH gives the boron-bridged dinuclear species Fc # 2 BBr with concomitant liberation of B 2 H 6 (Fc # = (C 5 Me 5 )Fe(C 5 H 4 )). The transformation is slow (48 h) but nevertheless provides yields of >85%. Fc # 2 BBr can conveniently be converted into the aminoborane Fc # 2 BNMe 2 by treatment with Me 3 SiNMe 2 . For an X-ray crystal structure analysis, Fc # 2 BNMe 2 was hydrolyzed to the borinic acid Fc # 2 BOH. A cross-coupling experiment using Et 3 SiH and an equimolar mixture of FcBBr 2 and Fc # BBr 2 led to the formation of the mixed product Fc(Fc # )BBr with high selectivity (Fc = (C 5 H 5 )Fe(C 5 H 4 )). Similar to the case for Fc # 2 BBr, Cym 2 BBr can be prepared from CymBBr 2 and Et 3 SiH (Cym = (OC) 3 Mn(C 5 H 4 )). In contrast to FcBH 2 , which exists only as transient intermediate on the way to Fc 2 BH, CymBH 2 is an isolable species. The compound was synthesized from a concentrated toluene solution of CymBBr 2 and excess neat Et 3 SiH at -78 °C and forms B-H-B-bridged dimers (CymBH 2 ) 2 in the solid state (X-ray crystallography). Our reactivity studies indicate that the Et 3 SiH-induced coupling reaction of derivatives L n M-(C 5 H 4 BBr 2 ) is fastest for electron-rich cyclopentadienyl complexes. Addition of NMe 2 Et to (CymBH 2 ) 2 affords the monomeric amine adduct CymBH 2 (NMe 2 Et). The reaction of (CymBH 2 ) 2 with HCC t Bu in a stoichiometric ratio of 1:4 (or slightly higher) results in a mixture of products from which the dinuclear hydroboration product (CymB(C(H)dC(H) t Bu)) 2 C(H)-C(H) 2 t Bu could be isolated and structurally characterized. To obtain the divinylborane CymB(C(H)dC(H) t Bu) 2 in high yield and pure form, (CymBH 2 ) 2 has to be dissolved in excess neat HCC t Bu.

Weakly Stabilized Primary Borenium Cations and Their Dicationic Dimers

“…Another bonding parameter of interest is the C–B bond distance of 1.58Å, which is only marginally shorter than the corresponding C–B bond in the starting carbene borane 2e (1.59Å). 13 The crucial B···B distance in 23 is 1.78Å, and is essentially identical to B···B distances measured by X-ray crystallography in neutral RBH 2 dimers (1.78-1.79Å) 14,15 as well as to the B···B distance in the parent B 2 H 6 determined by electron diffraction (1.77Å) 16 or X-ray methods (1.78Å). 17 A substantially shorter B···B distance has been established for a structure containing a B–B bond (X-ray,1.49Å; neutron diffraction, 1.48Å).…”

Aryl(hydro)boranes: versatile building blocks for boron-doped π-electron materials

“…Increasing the steric bulk of the reactants by switching from FcBBr 2 to Fc # BBr 2 (Fc # = 1′,2′,3′,4′,5′-pentamethylferrocenyl) significantly slows down the condensation reaction, but not to an extent that would allow the unambiguous identification of intermediate {Fc # B(H)Br} in the mixture. 83 Similar to the ferrocenyl(dibromo)boranes, CymBBr 2 transforms to Cym 2 BBr upon addition of Et 3 SiH (Cym = cymantrenyl). 83 In stark contrast to the ferrocenyl species, it is also feasible to generate and crystallise the dimeric dihydroborane (CymBH 2 ) 2 at low temperatures, even though {CymBH 2 } does not have a cyclic framework.…”

“…83 Similar to the ferrocenyl(dibromo)boranes, CymBBr 2 transforms to Cym 2 BBr upon addition of Et 3 SiH (Cym = cymantrenyl). 83 In stark contrast to the ferrocenyl species, it is also feasible to generate and crystallise the dimeric dihydroborane (CymBH 2 ) 2 at low temperatures, even though {CymBH 2 } does not have a cyclic framework. 83 The organometallic substituent needs to adopt a bridging position between two boron atoms in the intermediate state of the condensation reaction (cf.…”

A metal-mediated boron-centred isomerisation reaction via C–H activation

“…This reaction also proceeds in non-polar hydrocarbon solvents such as benzene or hexane at a slower rate (2 days). 12,13 The B-C6 distance of 1.639(3) Å remained unchanged from that of the precursor 4 [1.644(4) Å]. The 1 H NMR spectrum revealed four distinct signals between 4.57 and 4.76 ppm, which are attributed to a substituted cyclopentadienyl ligand.…”