Synthesis and Reactivity of Heterodinuclear Fe−Ni Complexes with a Bridging Alkoxysilyl Ligand. Crystal Structure of [(OC)₃Fe{μ-Si(OMe)₂(OMe)}(μ-dppm)NiMe]

Abstract

The new heterobimetallic complex (1) was obtained in 95% yield by reaction of [NiCl2(PPh3)2] in THF with K[Fe{Si(OMe)3}(CO)3(dppm-P)] at −78 °C. The analogous bromo and iodo complexes were also obtained; the latter is, however, less stable and could not be isolated pure. They display the first examples of a bridging alkoxysilyl ligand between Fe and Ni, and the μ2-η2-SiO bridge is also present in the methyl complex (4) and its phenyl analogue 5. The presence of the four-membered rings was confirmed by a crystal structure determination of 4. Treatment of 1 with excess (allyl)MgCl led to the expected bimetallic allyl complex (6). The rapid η3-allyl → η1-allyl → η3-allyl rearrangement is potentially assisted through stabilization of the coordinatively unsaturated Ni center by a SiO→Ni interaction. The bimetallic benzyl derivative 7 was also isolated. Purging a THF or benzene solution of 4 at room temperature with CO yielded after a few seconds the acyl complex (8), which readily decarbonylates. Its reaction with norbornadiene leads to the insertion product, which is thought to exist as an isomeric mixture with terminal or chelating acyl group (11 ⇌ 11‘). When complex 4 was reacted with t BuNC, rapid insertion occurred and further coordination of a terminal t BuNC ligand to Ni led to the iminoacyl complex (12). Complex 1 proved to be a more efficient catalyst (TON = 4100) for the dehydrogenative coupling of Ph3SnH than its mononuclear counterpart [NiCl2(PPh3)2] (TON = 1050). The maximum turnover frequency (TOF) was ca. 9800 h-1.

Palladium and Platinum Complexes Containing the Linear Tetraphosphine Bis[((diphenylphosphino)ethyl)phenylphosphino]methane

“…31 P{ 1 H} NMR (CDCl3): δ(P) 36.9 (br s, 1 JPtP ) 1703 Hz, 3 JPtP ) 37 Hz, 2 JPP ) 24 Hz, internal P), 40.0 (d, 2 JPP ) 7 Hz, 1 JPtP ) 1690 Hz, external P). 1 H NMR (CDCl3): δ(H) 2.09 (s, 6H, CH3), 2.15 (s, 6H, CH3), 1.58-1.73, 1.81-1.87, 2.03-2.08 (br m, PCH2CH2P), 2.58, 3.45 (br m, PCH2P), 6.61 (d, 3 JHH ) 7 Hz, 4H, CH-2,6), 6.83, (d, 3 JHH ) 7 Hz, 4H, CH-2,6), 7.01 (d, 3 JHH ) 7 Hz, 4H, CH-3,5), 7.07 (d, 3 JHH ) 7 Hz, 4H, 5),C6H5). HRMS (CsI added): exact mass calcd for 12 C69H68P4-Cs 195 Pt2 + , 1543.2622; obsd, 1543.2593.…”

“…This is found for the side-by-side dimers [M 2 X 2 (μ-dppm) 2 ] (M = Pd, Pt) and the many A-frame structures involving rhodium, iridium, palladium, and platinum . One or two dppm ligands have been employed also in the synthesis of heterobimetallic complexes . Indeed, we have used the [PtR(dppm- PP )(dppm- P )] + cations as precursors to a range of heterobimetallic derivatives …”

“…4 One or two dppm ligands have been employed also in the synthesis of heterobimetallic com-plexes. 5 Indeed, we have used the [PtR(dppm-PP)-(dppm-P)] + cations as precursors to a range of heterobimetallic derivatives. 6 We have made extensive studies of A-frame complexes of palladium and platinum.…”

Hydrocarbyl Ligand Transformations on Heterobimetallic Complexes

“…118 Migratory insertion reaction to give Fe-Ni(COMe) species is also seen when a nickel atom replaces the palladium or platinum in the Fe-Ni equivalents of 42 (Scheme 56). 119 The hemilabile trialkoxysilyl groups are not always required: the Fe-Pd complex [(OC) 4 Fe(µ-dppm)PdCl(Me)] (Fe-Pd) forms the Pd-bonded acetyl species [(OC) 4 Fe(µ-dppm)PdCl(COMe)] (Fe-Pd) when treated with CO. 120 When a Si(OSiMe 3 ) 2 R (R ) Me, 42h ; R ) OSiMe 3 , 42i) group replaces the Si(OMe) 3 group in the Fe-Pd systems shown in Scheme 56, the reaction proceeds further and the final products of the migratory insertions are the µ-siloxycarbene complexes 99 (Scheme 57). Labeling experiments with 13 CO indicate that the label is incorporated into the carbenoid carbon as well as onto the Pd-bonded CO group.…”

“…For example, the Fe-Ni complex 42c formally inserts t-BuNC into the Ni-Me bond to give 117a as shown in Scheme 69. 119 A µ-Si(OR) group is not always necessary as the related complex [(OC) 4 Fe(µ-Ph 2 PNHPPh 2 )PdClMe] (Fe-Pd) forms the Pd-bonded species [(OC) 4 Fe(µ-Ph 2 -PNHPPh 2 )-PdCl{C(NR)Me}] (Fe-Pd) when treated with RNC (R ) Bz, 2,4-Me 2 C 6 H 3 ). 120 The Fe-Pd complex 42d (Scheme 56) undergoes multiple isocyanide insertions with various isocyanide ligands.…”