Fulvalene, complexe

Deactivation of a homogeneous catalyst by dimerization can usefully be prevented by supporting the monomeric unit [note also that most multicenter catalysts require dissociation to an active monomeric form (/, p. 405 also Section VI)]. This concept has been used to maintain the hydrogenating activity of titanocene intermediates, which normally dimerize to inactive fulvalene complexes (334-336). Similarly maintained... 

A very interesting recent study describes the intramolecular disproportionation of homodinuclear and heterodinuclear fulvalene complexes in the presence of PMe3.88 Equation (14) shows one of the six reactions reported. In this case, initiation of the radical chain process was accomplished with a catalytic amount of the 19-electron reservoir complex [CpFe(C6Me6)], which reduces 13 to break the Ru—W bond and generate a 17-electron radical center (presumably at Ru). Addition of PMe3 to the Ru is followed by electron transfer to the reactant (13) to afford the zwitterionic product 14 and regenerate the radical intermediate. 

Many years later it was found that Na[C5H5] DME could be oxidatively coupled to provide dihydrofulvalene, using iodine as the oxidant, and that this provided access to fulvalene complexes. 

The P—H bonds of primary phosphines RPH2 add to zirconocene to give unstable zirconium phosphido hydrides CpZr(H)(PHR) from which C—H activation products such as fulvalene complexes [CpZr(/A-PHR)]2(rf r -QoHg) can be isolated.44 The addition of Ph2P(0)H to M(PEt3)3 (M = Pd, Pt) gives (21-X) the Pd derivative catalyzes the hydrophosphinylation of alkynes.45... 

In addition to fulvalene complexes, other bridges such as the bis(dimethylsilylclopentadienyl) ligand have been used to bridge dinuclear complexes." Other pendant groups have been attached to the cyclopentadienyl ligand, and these can lead to interesting complexes as well. The cyclopentadienyl phosphine system" shown in equation (18) is but one of the numerous examples. 

The bimetallic fulvalene complex CpZr(/u,-i7 V-C5H4—C5H4)(jit-Cl)2ZrCp reacts with tert-buty isocyanide to give Cp(Cl)Zr jLt-CioHgKju,-T/ T7 -C=N Bu ZrCp(Cl) (136) (344,345). During a sequence of insertion... 

The ionic fulvalene titanium complex [ CpTi(H2O) 2(/i-Ci0H8)(/i-O)]2+[OTP]2 l/2THF (Scheme 591) can be prepared as an air stable compound by the reaction of binuclear [CpTi(/i-H)]2(//-C10H8) with trifluoromethane-sulphonic acid in the presence of small amounts of water. A reaction intermediate is [TiCp(OTf)2]2(//-Ci0H8). The molecular structure of the fi-oxo aquo fulvalene complex has been confirmed by X-ray crystallography.1534... 

Reduction of Cp2ZrCl2 with 1.5equiv. of sodium amalgam affords the fulvalene complex CpZr(/r-Cl) 2(/r-C5H4-C5H4) 28.35 COMC(1995) summarized a number of phosphido, sulfide, imido, and alkyl complexes derived from 28. Cuenca and co-workers have since reported further investigations into the chemistry of 28, leading to new zirconium(iv) /(-imido. //-(r/2.r/2-N.N-hydrazido), and //-(r/ -C r/2-C,N-isocyanido) dinuclear fulvalene derivatives.36... 

In the absence of donor ligands, the binuclear zirconium fulvalene complex reacts with Ph3C[B(C6F5)4] to give the relatively inert (g-CH2)(g-CH3) doubly-bridged binuclear cationic complex 71 7550 (Equation (45)). This C-H activation process via ct-H elimination and loss of CH4 is facile even at — 60 °C. 

Half-sandwich complexes [Rh (Cp)(CO)(L)] with L = CO, PPha, PMes, and P(OPh>3 all reveal irreversible oxidation waves in cyclic voltammograms. In all cases, the intermediate 17 VE electron monocationic species couple to give dinuclear species. For L = CO and PPh3, the oxidation leads to formation of fulvalene complexes (87-89). This reaction could proceed via C—C coupling of two Cp ligands with a net loss of H2, followed by Rlu Rh bond formation [path (a) in Fig. 24]. 

A dinuclear Zr fulvalene complex is reported to react with Ph3C+B(C6F5)4 or FAB, even at —60 °C, with immediate elimination of methane to afford relatively inert /i-CHz complex 93 (eq 53). ° ... 

ONE AND TWO-ELECTRON OXIDATIONS OF BIMETALUC FULVALENE COMPLEXES STUDIED BY VOLTAMMETRY AND IR SPECTROELECTROCHEMISTRY... 

If the two redox sites in the fulvalene complex are chemically identical but strictly non-interacting, the electrode potential necessary to extract an electron from the monocation will be 0.036 V positive of that necessary to extract an electron from the neutral complex, i.e., AE (= E°2 EOi) = 36 mV.[7] The monocation would be called Class I mixed-valent in the Robin-Day classification scheme.[8]. If the monocation has a totally delocalized ground state (Class III), AE is much larger e.g.,... 

The present contribution discusses the oxidation and mixed-valency of dimanganese (and, to a lesser extent, dicobalt) fulvalene complexes which oxidize in discrete le steps. Different behavior is observed for dirhodium fulvalene complexes, in which 2e" waves are observed in oxidations that involve reversible making and breaking of M-M bonds. 

The fulvalene complex disubstituted with Co(ti -C3Hi2) / anodic behavior similar to that of biferrocene, with two le oxidations, AE = 228 mV. The fulvalene bis[Co(car-boranyl)] complex 11 [14] shows similar behavior, with AE = 270 mV for 11/llVn These complexes lack the convenient CO... 

Studies of General Interest.- MO calculations have been reported for complexes of the type CpH(L) H with a view to understanding the factors responsible for the acidic or hydrldic character of the M-H bond. Redistribution reactions that Involve exchange of Cp ligands between different CpM(L) complexes have been reviewed. A variety of bimetallic y-fulvalene complexes of Cr, Mo, W, Co, and Ru, including the mixed-metal complex [(OC) Mo-Ru(CO)2(y-fulvalene)],... 

The instability of the quasi-organometallic donor anion tetraphenylborate (Ph4B ) has been exploited in a number of photochemical [216-218] and photolithographic [219] applications. The role of tetraphenylborate is exemplified in the photoreduction of the dimeric cobalt(fulvalene) complex, i.e. 

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