Reaction of the Transition Metal Hydrides [Cp*MH₂]₂ (Cp* = η⁵-C₅Me₅; M = Fe, Ru) with BH₃·THF to Yield Metallaboranes. Improved Kinetic Control Leads to Novel Ferraboranes

Abstract

The reactions of [Cp*MH 2 ] 2 , Cp* ) η 5 -C 5 Me 5 ; M ) Fe, Ru, with BH 3 ‚THF have been explored. As with [Cp*RuCl 2 ] 2 , [Cp*RuH 2 ] 2 readily reacts with borane to generate nido-1,2-(Cp*RuH) 2 B 3 H 7 . In contrast to the chloride, intermediates are detectible in the hydride reaction and product selectivity is higher. Benefits of the apparently lower reaction barrier appear in the reaction of [Cp*FeH 2 ] 2 with BH 3 ‚THF. The formation and isolation of the novel hydrogen-rich ferraborane arachno-1-Cp*FeB 4 H 11 from the iron hydride contrasts with the production of pentamethylferrocene from a pentamethylcyclopentadienyl iron halide. This metastable ferraborane has been characterized spectroscopically as well as by reaction with Co 2 (CO) 8 to give a good yield of the more stable derivative nido-1-(Cp*Fe)-2-{Co(CO) 3 }B 4 H 8 by metal fragment addition. The latter compound has been spectroscopically characterized in solution as well as in the solid state by a single-crystal X-ray diffraction study as an example of a mixed metal dimetallahexaborane.

Synthesis and crystal structures of two (cyclopentadienyl)titanium(III) hydroborate complexes, [Cp∗TiCl(BH4)]2 and Cp2Ti(B3H8)

“…A few examples of the reverse reaction have been described: [Mo(CO) 4 (B 3 H 8 ) À ] [15], Cp * ReH 3 (B 3 H 8 ) [16], and WH 3 (B 3 H 8 [17] have been prepared by treating [Mo 2 H(CO) 10 À ], Cp * ReH 6 , and WH 6 (PMe 3 ) 3 with BH 3 Á thf, respectively, and (C 5 H 4 -i-Pr)WH 3 (B 3 H 8 ) has been made by treating (C 5 H 4 -i-Pr)WCl 4 with LiBH 4 [18]. In addition, other B 3 H x fragments (especially those with x = 6 or 7) can be made by adding BH 3 to a transition metal hydride or chloride [19][20][21][22][23][24][25][26][27][28].…”

Formation of ferraboranes from pentaborane(9) or BH3·thf and an electron-rich cyclopentadienyl iron phosphine hydride

“…The yield of 3 falls to zero if a large excess of BH 3 AE thf is used. The decomposition of monocyclopentadienyl iron compounds to the thermodynamically very stable ferrocene has been reported for the reaction of the anion [Fe(g 5 -C 5 H 5 )(C 2 H 4 ) 2 À ] with trimethylphosphonium chloride [44]. This ''thermodynamic sink'' is not available in the reaction of monocyclopentadienyl cobalt compounds with BH 3 AE thf since the formation of the 19-electron [Co(g-C 5 H 5 ) 2 ] is far less favourable.…”

Dehydrogenation of iron amido-borane and resaturation of the imino-borane complex

“…Such ferrous borohydrides have been documented only rarely, 31 since they are prone to form polynuclear iron borate clusters. 32,33 The 11 B NMR spectrum of the reaction solution shows a quintet at δ 15.4 ( J BH = 88 Hz) for the BH 4 − ligand of 1 , and this stands in contrast to the signal at δ −32.0 observed for Bu 4 NBH 4 . Upon storing the reaction mixture at −30 °C overnight, single crystals suitable for X-ray diffraction were obtained.…”

“…Such ferrous borohydrides have been documented only rarely, 31 since they are prone to form polynuclear iron borate clusters. 32,33 The 11 B NMR spectrum of the reaction solution shows a quintet at d 15.4 (J BH ¼ 88 Hz) for the BH 4…”