Novel Metal-to-Metal Silyl-Migration Reactions in Heterometallic Complexes

Abstract

An unprecedented, intramolecular metal-to-metal silyl ligand migration reaction has been discovered in a series of phosphido-bridged iron-platinum complexes and which may be triggered by an external nucleophile. Thus, reaction of solutions of [(OC)3-(R1/3Si)Fe(mu-PR2R3)Pt(1,5-COD) (1a R1 = OMe, R2 = 3 = Ph; 1b R1 = OMe, R2 = R3 = Cy; 1c R1 = Ph, R2 = R3 = Ph; 1d R1 = Ph, R2 = R3 = Cy; 1e R1 = Ph, R1 = H, R3 = Ph) in CH2Cl2 with CO rapidly afforded the corresponding complexes [(OC)4Fe(mu-PR2R3)Pt(SiR1/3)-(CO)] (2a-e) in which the silyl ligand has migrated from Fe to Pt, while two CO ligands have been ligated, one on each metal. When 1a or 1c was slowly treated with two equivalents of tBuNC at low temperature, quantitative displacement of the COD ligand was accompagnied by silyl migration from Fe to Pt and coordination of an isonitrile ligand to Fe and to Pt to give [(OC)3-(tBuNC)Fe(mu-PPh2)Pt[Si(OMe)3](CNtBu)] (3a) and [(OC)3(tBuNC)-Fe(mu-PPh2)Pt[SiPh3](CNtBu)] (3c). Reaction of 2a with one equivalent of tBuNC selectively led to substitution of the Pt-bound CO to give [(OC)4-Fe(mu-PCy2)Pt[Si(OMe)3](CNtBu)] (4b), which reacted with a second equivalent of tBuNC to give [(OC)4Fe(mu-PCy2)-Pt[Si(OMe)3](CNtBu)2] (5b) in which the metal-metal bond has been cleaved. Opening of the Fe-Pt bond was also observed upon reaction of 3a with tBuNC to give [(OC)3(tBuNC)-Fe(mu-PPh2)Pt[Si(OMe)3](CNtBu)2] (6). The silyl ligand migrates from Fe, in which it is trans to mu-PR2R3 in all the metal-metal-bonded complexes, to a position cis to the phosphido bridge on Pt. However, in 5a,b and 6 with no metal-metal bond, the Pt-bound silyl ligand is trans to the phosphido bridge. The intramolecular nature of the silyl migration, which may be formally viewed as a redox reaction, was established by a cross-over experiment consisting of the reaction of 1a and 1d with CO; this yielded exclusively 2a and 2d. The course of the silyl-migration reaction was found to depend a) on the steric properties of the -SiR1/3 ligand, and for a given mu-PR2R3 bridge (R2 = R3 = Ph), the migration rate decreases in the sequence Si(OMe)3> SiMe2Ph> SiMePh2>>SiPh3; b) on the phosphido bridge and for a given silyl ligand (R1 = OMe), the migration rate decreases in the order mu-PPh2 >> mu-PHCy; c) on the external nucleophile since reaction of 1c with two equivalents of P(OMe)3, P(OPh)3 or Ph2PCH2C(O)Ph led solely to displacement of the COD ligand with formation of 11a-c, respectively, whereas reaction with two equivalents of tBuNC gave the product of silyl migration 3c. Reaction of [(OC)3-[(MeO)3Si]Fe(mu-PPh2)Pt(PPh3)2] (7a) with tBuNC (even in slight excess) occurred stereoselectively with replacement of the PPh3 ligand trans to mu-PPh2, whereas reaction with CO led first to [(OC)3((MeO)3Si)Fe(mu-PPh2)Pt(CO)-(PPh3)] (8a), which then isomerized to the migration product [(OC)4Fe(mu-PPh2)Pt[Si(OMe)3](PPh3)] (9a). Most complexes were characterized by elemental analysis, IR and 1H, 31P, 13C, and 29Si NMR spectroscopy, and in five cases by X-ray diffraction.

Intramolecular d10–d10 interactions in heterometallic clusters of the transition metals

“…This complex also undergoes dynamic behaviour in solution, but this time the motion involves a sliding of the Pd centre along the Fe-Hg-Fe chain. Fe has migrated to platinum, a rare event [167][168][169][170][171]. The possibility of reversible isomerization involving the Pt analog of 51 has been discussed 157.…”

Crystal structure of tricarbonyl(μ-diphenylphosphido-κ2P:P)(methyldiphenylsilyl-κSi)bis(triphenylphosphane-κP)iron(II)platinum(0)(Fe—Pt)

“…Whereas in all four SiPh 3bearing complexes the silyl group is in a trans-position with respect to the PPh 2 bridge, the SiPh 2 Me ligand of (I) is roughly colinear with the Fe-Pt vector, the Si-Fe-Pt angle being 169.07 (3) . The P-Fe-Si angle in (I) amounts to 119.32 (3) , whilst that of [(OC) Braunstein et al, 2000] is close to a theoretical linear trans-arrangement.…”

“…2. The iron and platinum atoms are linked by a phosphide bridge and a formal metal-metal bond, whose Fe-Pt separation of 2.7738 (4) Å is somewhat longer, probably because of steric hindrance between the Ph groups of the PPh 3 and PPh 2 ligands, than those reported for [(OC) 3 Fe(SiPh 3 )(-PPh 2 )Pt(PMe 3 ) 2 ] [Fe-Pt = 2.701 (2) Å ; Knorr et al, 1994], [(OC) 3 Fe(SiPh 3 )(-PPh 2 )Pt{Ph 2 C(=CH 2 )PPh 2 }] [Fe-Pt = 2.659 (2) Å ; Knorr et al, 1994], [(OC) 3 Fe(SiPh 3 )(-PPh 2 )Pt(C N-Xylyl)(PPh 3 )] [Fe-Pt = 2.631 (1) Å ; Braunstein et al, 2000] and [(OC) 3 Fe(SiPh 3 )(-PPh 2 )Pt(CO)(PPh 3 )] [Fe-Pt = 2.620 (2) Å ; Reinhard et al, 1993]. The Fe-Si bond length of 2.3497 (9) Å is quite comparable with the Fe-Si bond lengths in the latter four compounds, which range from 2.330 (1) to 2.356 (3) Å .…”

Synthesis and structures of bridged biscyclopentadienyl diiron complexes

“…Much attention has been focused on the unsymmetrical dinuclear transition metal complexes due to their distinctive properties caused by connecting two metal fragments with diverse characteristics [1][2][3][4][5][6][7][8][9]. Fulvenes are fascinating organic ligands in view of their different coordination modes toward transition metals.…”