Synthesis and Electrochemical Properties of C₅H−Bridged Bimetallic Iron, Ruthenium, and Osmium Complexes

Abstract

Treatment of [CpOs(PPh3)2]BF4 in THF with 0.5 equiv of HC⋮CCH(OH)C⋮CH followed by Al2O3 gave the C5H-bridged compound [Cp(PPh3)2OsCCCHC⋮COs(PPh3)2Cp]BF4. The analogous iron complex [Cp(dppe)FeCCCHC⋮CFe(dppe)Cp]BPh4 has been prepared similarly. The structure of [Cp(PPh3)2OsCCCHC⋮COs(PPh3)2Cp]BF4 has been confirmed by X-ray diffraction. The electrochemical properties of [Cp(dppe)FeCCCHC⋮CFe(dppe)Cp]BPh4, [Cp(PPh3)2RuCCCHC⋮CRu(PPh3)2Cp]BF4, and [Cp(PPh3)2OsCCCHC⋮COs(PPh3)2Cp]BF4 have been studied by cyclic voltammetry.

Repercussion of a 1,3-Hydrogen Shift in a Hydride-Osmium-Allenylidene Complex

“…The Os–C(1), C(1)–C(2), and C(2)–C(3) distances of 1.858(6), 1.261(8), and 1.351(8) Å, respectively, compare well with those reported for the previously structurally characterized osmium-allenylidene complexes. 9 , 21b , 23 In agreement with them, C(1)–C(2) and C(2)–C(3) are about 0.05 Å shorter and longer, respectively, than the bond length expected for a carbon–carbon double bond (about 1.30 Å), which suggests a notable contribution of the canonical form [M] − —C≡C—C + Ph 2 to the structure of the C 3 -chain. In accordance with the presence of hydride and allenylidene ligands, the IR spectrum of the molecule contains the corresponding characteristic ν(Os–H) and ν(C=C=C) bands at 2090 and 1863 cm –1 .…”

Recent Developments in the Reactivity of Allenylidene and Cumulenylidene Complexes

“…a) Dinuclear cationic complexes of three types (Figure 2): ( i ) the osmium(II) derivative [(η 5 ‐C 5 H 5 )(PPh 3 ) 2 Os{=C=C= C(H)−C≡C−Os(η 5 ‐C 5 H 5 )(PPh 3 ) 2 }][BF 4 ] ( A );21 ( ii ) the mixed‐valence ruthenium(II)−ruthenium(III) complex [Ru(=C=C=Rc)(η 5 ‐C 5 H 5 )(DPPE)][BF 4 ] 2 [Rc = (μ 2 ‐η 6 :η 5 ‐C 5 Me 4 )Ru(η 5 ‐C 5 H 5 )] containing a half‐sandwich ruthenium(III) fragment bonded to a (cyclopentadienylidene)ethylidene group which acts as the bridging chain to the (η 5 C 5 H 5 )Ru moiety ( B ) 22. Another example of this type is the dimetallic iron(II)−chromium(0) complex [(CO) 2 (η 5 ‐C 5 H 5 )Fe(μ‐η 1 :η 7 ‐C 2 C 7 H 6 )Cr(CO) 3 ][BF 4 ] ( C ) although structural parameters of the Fe−C α −C β −C γ chain indicate that the bridging moiety can be better described as a substituted tropylium alkynyl group;23 and ( iii ) the bis(allenylidene)dirhodium(I) complex {[(P i Pr 3 ) 2 {Ph( o ‐Tol)C=C=C=}Rh] 2 (μ‐1,3‐N 3 )} + ( D ) in which the two allenylidene groups, both rhodium atoms and the bridging azide ligand form an unusual eleven‐membered chain 24…”

“…As expected, typical low field signals are found in the range δ ≈︁ 255−320. The following features deserve to be mentioned: a) although the resonance for the dinuclear iron(II) complex [(η 5 C 5 H 5 )(PPh 3 ) 2 Fe{=C=C=CH−C≡C−Fe(PPh 3 ) 2 (η 5 C 5 H 5 )}][BF 4 ] appears as usual (δ Cα = 223.3), an high field chemical shift is shown by the corresponding resonance in the analogous osmium derivative (δ Cα = 196.2);21 b) a significant shielding effect on the C α nucleus is observed in allenylidenes containing donor groups of the type trans ‐[RuX{=C=C=CR 1 R 2 }(DPPE) 2 ][PF 6 ], i.e. X = Cl; R 1 = H; R 2 = p ‐NMe 2 C 6 H 4 (δ Cα = 265.7) vs. X = Cl; R 1 = H; R 2 = Ph (δ Cα = 321.07), X = Cl; R 1 = R 2 = p ‐OMeC 6 H 4 (δ Cα = 288.4) vs. X = Cl; R 1 = R 2 = Ph (δ Cα = 308.58), and R 1 = H; R 2 = CH=CH( p ‐NO 2 C 6 H 4 ) (δ Cα = 322.77);10 c) although the order δ Cα > δ Cβ > δ Cγ is usually found for most of the allenylidene complexes, an inversion of the sequence of the chemical shifts has been reported in several cases, i.e.…”

“…This charge is found to decrease towards the C γ atom. Brief accounts of theoretical calculations on the dinuclear complexes [(η 5 ‐C 5 H 5 )(PH 3 ) 2 Ru{=C=C=C(H)−C≡C−Ru(PH 3 ) 2 (η 5 ‐C 5 H 5 )}] + 21 and [(PH 3 ) 4 IMn=C=C=C=C=MnI(PH 3 ) 4 ]29a have also been reported. More recently,40 density‐functional calculations have been performed on the metallacumulenylidene complexes [Cr{(=C) n H 2 }(CO) 5 ] ( n = 2−9) showing, as for the above‐mentioned examples, that the electrophilic and nucleophilic attacks are frontier orbital controlled.…”

Unprecedented Coupling of Allenylidene and Diynyl Metal Complexes: A Bimetallic Ruthenium System with a C7 Conjugated Bridge

“…The three compounds undergo a well‐defined one‐electron reversible oxidation wave followed by an almost reversible or irreversible second oxidation wave consistent with the doubly oxidized species undergoing subsequent chemical reactions. To a first approximation, these two oxidation steps could be viewed as essentially involving the two Ru II /Ru III couples 5b. 8d, 12 The large separation of the processes (Δ E° =650 mV, K c =exp(Δ E° F / RT )=1.27×10 11 for 3 b 2a) is attributable to a combination of phenomena such as strong electronic coupling, columbic repulsion, and/or structural distortion through the oxidations.…”