Aryldihydroborane Coordination to Iridium and Osmium Hydrido Complexes

Abstract

A series of iridium dihydroborate complexes [(tBuPOCOP)­IrH­(κ2-H2BHR)] (tBuPOCOP = κ3-C6H3-1,3-[OPtBu2]2; R = Mes = 2,4,6-Me3C6H2; R = Dur = 2,3,5,6-Me4C6H) and [LIrH­(κ2-H2BHDur)] (L = tBuPCP = κ3-C6H3-1,3-[CH2PtBu2]2, L = η5-C5Me5) and an osmium dihydroborate compound [OsH­(κ2-H2BHDur)­(CO)­(PiPr3)2] have been prepared by using two different synthetic strategies. The first approach is based on direct borane coordination to the metal center, whereas the second is based on a salt-elimination protocol using the lithium salts Li­[H3BR] (R = Mes or Dur) and the corresponding metal halides. The compounds have been characterized by multinuclear NMR and IR spectroscopy and X-ray diffraction analysis. The results constitute the first syntheses of κ2-σ:σ-dihydroborate complexes featuring bulky aryl groups.

Synthesis and Characterization of PBP Pincer Iridium Complexes and Their Application in Alkane Transfer Dehydrogenation

“…Radius, Braunschweig, et al discussed the limiting structural motifs for complexes of [R 2 BH 2 ] − fragments with transition metals (Chart ). They argued that a more Lewis acidic boron center favors structural type A (κ 2 -dihydroborate) over B (σ-B–H complex of a metal hydride), whereas a more electron-rich metal would favor the higher valence type C (boryl/dihydride). It should be noted that type B may correspond to two degenerate forms ( B and B′ ), which may average out to a more symmetric structure: for example, by NMR spectroscopy.…”

Steric Effects Dictate the Formation of Terminal Arylborylene Complexes of Ruthenium from Dihydroboranes

“…The 11 B NMR spectrum of 11 showed a broad signal at δ =21.1 ppm and the 1 H NMR spectrum revealed signals at δ =−19.83 and −6.37 ppm for terminal (Ir‐bound) and bridging hydrides, respectively, along with a broad peak at δ =8.47 ppm for the terminal B−H. The solid‐state structure of 11 , as shown in Scheme , exhibits a tetrahedral arrangement of the boron center, and the Ir−B distance (2.237(3) Å) is similar to other related iridium dihydroborate systems, such as [( t BuPCP)IrH(κ 2 ‐H 2 BHDur)], (2.283(2); t BuPCP: κ 3 ‐C 6 H 3 ‐1,3‐[CH 2 P t Bu 2 ] 2 ) [(Cy 3 P) 2 Ir(H) 2 (κ 2 ‐H 2 BH⋅NMe 3 )][B m Fxyl 4 ], (2.207(7)), and [(SIMes) 2 Ir(H) 2 (κ 2 ‐H 2 BH⋅NMe 2 H)][B m Fxyl 4 ] (2.21(4) Å; SIMes: 1,3‐bis(2,4,6‐trimethylphenyl)imidazolidin‐2‐ylidene).…”

“…[10] Even thougho xidative addition of the BÀHb ond of (RO) 2 BH to metal centers is facile, [11] there are few examples of oxidative addition of the BÀHb onds of dihydroboranes [12] which in most cases result in relativelys table k 2 -bis(s)-borane complexes, preventingt he oxidative addition of the BÀHb onds. [13] Nevertheless, the oxidative addition of both BÀHb onds of ad ihydroborane ([MesBH 2 ] 2 )w as achieved by Alcaraz, Sabo-Etienne,a nd co-workersi nt he synthesis of ab orylene complex using the ruthenium-dihydrogen complex [Ru(PCy 3 ) 2 HCl(H 2 )]. [14] The extensive work on both transition-metal-bound and metal-free borylenes has suggested that addition of further (usuallya liphatic)g roups to boron-bound aryl units is ap rerequisite for borylene formation.…”

Selective C–F and C–H Activation of Fluoroarenes by Fe(PMe3)4 and Catalytic Performance of Iron Hydride in Hydrosilylation of Carbonyl Compounds

“…A hydrido cobalt intermediate as a possible C–H bond activation product in the study of selective C–F/C–H bond activation of C 6 F 5 H with Co­(PMe 3 ) 4 was proposed on the basis of the observation of in situ IR and 1 H NMR spectra, but an experiment to isolate the hydrido cobalt intermediate also failed . Except for the C–H activation pathway, direct reduction is also feasible in synthesizing metal hydrides according to refs and . The reaction of bromopentafluorobenzene with Fe­(PMe 3 ) 4 in diethyl ether at room temperature gave a red solution.…”