Anionic metal carbonyls

Bimetallic Complexes. There are two types of bimetaUic organometaUic thorium complexes those with, and those without, metal—metal interactions. Examples of species containing metal—metal bonds are complexes with Ee or Ru carbonyl fragments. Cp ThX(CpRu(CO)2), where X = Cl or 1, and Cp7Th(CpM(CO)2), where M = Ee or Ru, have both been prepared by interaction of CP2TI1X2 or Cp ThCl [62156-90-5] respectively, with the anionic metal carbonyl fragment. These complexes contain very polar metal—metal bonds that can be cleaved by alcohols. 

Azolides are also capable to acylate anionic metal carbonyl compounds. For instance, disodium tetracarbonylferrate as well as the corresponding ruthenium and osmium compounds can be formylated with formylimidazole in the presence of boric acid methyl ester ... 

Prior to our studies it was recognized that ion pairing with anionic metal carbonyls could promote CO insertion and related reactions (14-16). Both kinetic and non-kinetic evidence suggests the importance of ion pairs in these types of reactions (14,17). For example, a small cation was found to greatly accelerate the CO insertion reaction relative to the same reaction with a large cation, equation 6 (14). 

Darensbourg et al. have conducted extensive studies of the nucleophilic reactivity of a series of anionic metal carbonyl hydrides [24], which have been used for the reduction of alkyl halides [25], acyl chlorides [26], and ketones [27]. The... 

Several anionic metal carbonyl hydrides stoichiometrically convert acyl chlorides to aldehydes. The anionic vanadium complex [Cp(CO)3VH] reacts quickly with acyl chlorides, converting them to aldehydes [44]. Although no further reduction of the aldehyde to alcohol was observed, the aldehydes reacted further under the reaction conditions in some cases, so a general procedure for isolation of the aldehydes was not developed. 

Other mechanisms for the synthesis of alkylformates, not via formic acid esterification, are possible. Hydrogenation of C02 to CO, followed by catalytic car-bonylation of alcohol, would produce alkyl formate. This mechanism seems more likely for the anionic metal carbonyls because they are known catalysts for alcohol carbonylation. However, Darensbourg and colleagues [64, 74, 85] showed... 

Boron-bonded p -borazine complexes of transition metals have been prepared by two different approaches (a) nucleophilic substitution of B,fi, fi"-trichloro-borazine with an anionic metal carbonyl reagent and (b) oxidative addition of a B-Br bond of 5,5, B"-tribromoborazine to a zerovalent group 10 complex (see examples in Scheme 9.2). 

Metal-metal bonding is also known between different metals. Me3Sn—Fe(TPP) made from [Fe (TPP)]- is diamagnetic and probably contains an Sn,v—Fe" bond.194 123 Reaction of anionic metal carbonyls and In(Por)Cl gives metal-bonded complexes which show characteristic hyper-type spectra (L., 440 nm) (Scheme 26).124 The precedent of this type of metathesis is the unexpected formation of (TPP)Sn—Mn(CO)4—Hg—Mn(CO)s from Sn(TPP)Cl2 and sodium amalgam reduced [Mn(CO)5]. 125 In this compound, the linear Mn—Hg—Mn moiety is bonding to the Sn atom through the tetracarbonylated Mn and parallel to the macrocycle (Scheme 27). 

Supported nanoclusters have been prepared by decarbonylation of neutral or anionic metal carbonyl clusters on supports. The decarbonylation chemistry is not fully understood. The chemistry accompanying removal of the CO ligands from metal carbonyl clusters on metal oxides evidently involves hydroxyl groups or water on the surface of the metal oxide. 

The chemistry of haloalkynes with low-valent metal complexes has been reviewed.142 Two competing reactions of anionic metal carbonyls [M(CO) ] with halo-alkynes are (i) abstraction of X+ to give MX(CO) and (ii) nucleophilic displacement of X- to give M(C=CX)(CO) and M(CO) 2(ji-C=C). A recent study of reactions of haloalkynes with [M(CO)3Cp ]- (M = Cr, Mo, W Cp = Cp, Cp )] has clarified the reaction conditions, which are determined by the nucleophilicity of the anionic metal carbonyl and the electron-withdrawing power of any substituent on the C=C triple bond. Cross-coupling of the anion with a chloroalkyne is catalyzed by palladium.143... 

Several anionic metal carbonyls were used for intramolecular cyclization of l-(3-bromo-l-propynyl)-ketones 33. Among these salts, CpWlCOlsNa was the most effective in yielding a metalated fused 77 -2,5-dihydro-3-furyl complex 34. Demetalation of the organometallic product by (NH4)2Ce(N03)6 in MeOH/CH2Cl2 under a CO atmosphere provided fused 3-(methoxycarbonyl)-2,5-dihydrofurans 35 in yields of 50-60% (Scheme 37) <1996JOC3245>. 

Reactions involving nucleophilic attack on coordinated ligands are promoted by very polar solvents that stabilize anions. Metal carbonyls are also attacked by strong nucleophiles (RLi) to give the Fischer carbene complexes qv below. Section A 1.4),... 

Studies of the use of anionic metal carbonyl hydrides m the catalytic conversion of CO2, Hj. and alcohols, have been performed by Evans [I69. who found that ((N(PPh3)2)(HFe3(CO) ) and(llNEt3)(HFej(CO) ) were more effective than (N(PPh3)5>(HFc(CO)4>. with a maximum conversion of 5.8 mol formate per mol anion in a four-day reaction. 

Reactions of anionic metal carbonyl complexes with certain onium compounds are also related mechanistically, a neutral molecule rather than an anion being displaced from the organic precursor, e.g. ... 

Table 6. Comparison of isoelectronic neutral and anionic metal carbonyl complexes.

Heterobimetallic complexes have recently attracted considerable attention in light of the promise of enhanced reactivity as a result of the cooperativity between adjacent, but electronically different, metal centers. A large number of these bimetallic compounds have been synthesized by the reactions of organometallic halides with anionic metal carbonyls. Here, we describe an extension of this route to the synthesis of hydride rich. Os—Zr and Os—Rh complexes by the reaction of organometallic halides with a metal poly hydride anion. These preparations demonstrate the synthetic utility of transition metal polyhydride anions. 

The catalysts or catalysts precursors employed in these studies were anionic group 6 carbonyl complexes ( ) or group 8 metal carbonyl clusters (37— 0) where reaction conditions were 500 psi (CO2/H2) and 125 C. For the group 6 metal catalysts, the turn-over numbers obtained for the methyl formate production were ca. 15 using methanol as solvent for a 24 hour period. The anionic metal carbonyls examined as catalysts precursors included HM2(CO)io , HC02M(C0)5, and CH3C02M(C0)s as their PPN salts (PPN = bis(triphenylphosphine)-iminium and M Cr or W). The proposed reaction pathway is depicted in Scheme 3. 

A great deal of mechanistic investigations were done on the reaction with anionic metal carbonyls such as WCI(CO)51 as catalysts.61,62 Although such studies were extremely helpful in clarifying the way C02 was transformed to formate esters, the process itself cannot be regarded practical. 

Anion-exchange resins can be used as reagents.242 They are commercially available with acetate, borohydride, bromide, chloride, dichromate, iodide, and periodate anions. Metal carbonyl-containing anions such as Co(CO)7,... 

The majority of simple Lewis acid adducts of terminal carbonyls is formed with anionic metal carbonyls. But the above example demonstrates that... 

Reaction of the anionic metal carbonylates with alkyl carbocations causes an increase in stretching frequency of approximately 50 to 100 cm-1 in the... 

The reductive cleavage of M—M bonds can be achieved by a variety of reducing agents such as Na-Hg, Na benzophenone ketyl, and in some instances anionic metal carbonyls. These reagents would be expected to react by an outer sphere electron transfer mechanism. This does not preclude the possibility that the electrons are being transferred through the carbonyls to the metal centers. 

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