Synthesis of Metal-Alkyl Complexes

A disadvantage of the synthesis of metal-alkyl complexes by transmetallation is the potential for nucleophilic attack to occur at ancillary ligands. Carbonyl ligands are particularly vulnerable to nucleophilic attack, as shown in Equation 3.4, and described in more detail in Chapter 11. However, the extent to which this process competes with transmetallation depends on the electronic property of the metal. Thus, some carbonyl halides can be converted into alkyl carbonyl complexes (Equation 3.5). In addition, electron transfer from electron-rich carbon nucleophiles can limit the yields of transmetallation processes. 

Carbonylate complexes have many useful synthetic applications. Typical reactions involve nucleophilic attack of the metal anion on a positive center (alternatively viewed as an electrophilic attack on the metal). The synthesis of ntctal alkyl complexes has been referred to earlier (fiqs. 15.46 and 15.47). Other examples include ... 

Indeed, Mann s studies initiated an explosion of interest in transition metal phosphine chemistry. Chatt was Mann s student, and it is interesting to reflect that Chatt employed transition metal salts as a means of derivatising tertiary phosphines. Little did they realise how this area would expand Chatt s influence on metal-phosphine chemistry was profound, and out of it sprung the employment of phosphine complexes as tools for investigations into metal hydrides, nitrogen fixation, the stabilisation of unusual oxidation states, synthesis of metal alkyls and aryls, and the immense practical area of homogeneous and heterogen-... 

Metal formyl complexes have been proposed as important intermediates in the metal-catalyzed reduction of CO by H2 1,2, 3, 4). While the insertion of CO into alkyl and aryl carbon-metal bonds is well known (5), the insertion of CO into a metal-hydrogen bond to give a metal formyl complex has not been observed. (The intermediacy of metal formyl compounds in the substitution reactions of metal hydrides has been considered.) To ascertain the reasons for the failure to observe metal formyl complexes in the reactions of metal hydrides with CO, we have developed a new synthesis of metal formyl complexes and have studied their properties. 

Our group has explored in detail the reactivity of 82 and the dicyclohexylphos-phino analog 84 (Scheme 6.19). These Pt chloride complexes were utiHzed as precursors for the synthesis of Pt alkyl complexes and cations of the type [(PSiP)Pt]", with the goal of accessing highly reactive metal complexes that would engage in E-H bond activation chemistry [77]. Indeed, square planar Pt alkyl and aryl complexes of the type (R -PSiP)PtR (85, R = Ph, R = CH2Ph 86,... 

Transition-metal-silyl complexes are also formed by the reactions of metal-alkyl complexes with silanes to form free alkane and a metal-silyl complex. Two examples are shown in Equations 4.114 and 4.115. ° The synthesis of silyl complexes by this method has been accomplished with both early and late transition metal complexes. The formation of metal-silyl complexes from late-metal-alkyl complexes resembles the hydrogenolysis of metal-alkyl complexes to form metal hydrides and an alkane. The mechanisms of these reactions are discussed in Chapter 6. In brief, these reactions with late transition metal complexes to form silyl complexes typically occur by a sequence of oxidative addition of the silane, followed by reductive elimination of alkane. An example of this is shown in the coupling of 1,2-bis-dimethylsilyl benzene with a dimethyl platinum(II) complex (Equation 4.114). Similar reactions occur with d° early metal complexes by a a-bond metathesis process that avoids these redox events. For example, the reaction of Cp ScPh with MesSiH, has been shown to proceed through this pathway (Equation 4.115). ... 

The structural consequences of bonding for carbene complexes are discussed. Photochemical reactions of metal alkyl complexes result in very reactive intermediates that can be trapped and used preparatively. Matrix isolation studies of organometallic intermediates are considered in detail. Transition metals in organic synthesis for the year 1982 are reviewed extensively and a further article concerns a-(1,n)-alkanediy1 complexes. ... 

Dithiophosphato metal complexes are usually prepared by metathesis of metal halides with alkali metal or ammonium salts. A convenient method uses the redox reaction of his th iophosphory 1 )d is ulfanes (RO)2(S)PSSP(S)(OR)2, with metal species in low oxidation states resulting in the insertion of the metal into the sulfur-sulfur bond.24 Recently it was used for the synthesis of long alkyl chain, liquid platinum(II) dithiophosphates25 and for the synthesis of Ru (CO)2[S2P(OPr%]2 from Ru3(CO)i2 with (Pr 0)2(S)PSSP(S)(0Pr,)2.26... 

The well-established chemistry of alkide abstraction by B(C6F5)3 allows the facile synthesis of betaine-type complexes where the perfluoroarylborate counteranion is covalently attached to the metal cation via either a reactive alkyl group or an ancillary Cp ligand (Scheme For example, B(G6Fs)3 is added exclusively at a terminal GH2... 

As mentioned above, reactions of this type have been widely used in the synthesis of macrocyclic ligands. Indeed, some of the earliest examples of templated ligand synthesis involve thiolate alkylations. Many of the most important uses of metal thiolate complexes in these syntheses utilise the reduced nucleophilicity of a co-ordinated thiolate ligand. The lower reactivity results in increased selectivity and more controllable reactions. This is exemplified in the formation of an A -donor ligand by the condensation of biacetyl with the nickel(n) complex of 2-aminoethanethiol (Fig. 5-78). The electrophilic carbonyl reacts specifically with the co-ordinated amine, to give a complex of a new diimine ligand. The beauty of this reaction is that the free ligand cannot be prepared in a metal-free reac-... 

The synthesis of cyclopropyl carbyne complexes follows the general Fischer synthesis of carbyne complexes from alkoxycarbene complexes typical of transition metals of group 6 (Cr, Mo, W). Thus, addition of cyclopropyllithium to chromium and tungsten hexacar-bonyl followed by alkylation of the acylmetallate intermediate with triethyloxonium fluo-roborate gave cyclopropyl ethoxycarbene complexes which, upon subsequent reaction with boron tribromide at -25 °C, afforded the corresponding /ra 5 -bromotetracarbonyl cyclopropylcarbyne complexes (equation 91). However, whereas the monotungsten... 

Liu, B., Ctii, D.M., Ma, 1. et al. (2007) Synthesis and reactivity of rare earth metal alkyl complexes stabilized by aniUdo phosphinimine and amino phosphine ligands. Chemistry —A European Journal, 13, 834. 

The synthesis of the zinc complex 115 according to Scheme 3 presents an efficient alternative to the previous method based on reduction of carbon diselenide by sodium metal <1990JCD115>. Compounds 22, 98-101, and 116 containing either (2-methoxycarbonyl)ethyl or 2-cyanoethyl as thiolate protecting groups are versatile compounds for the synthesis of a large selection of functionalized tetraselenafulvalenes via the (1) base-promoted deprotection and (2) thiolate alkylation protocol. 

The protolysis route also promises to provide general access to cationic early-metal alkyl complexes in non-CpjM environments. Bochmann has recently reported the synthesis of [Zr(CH2Ph)3][BPh4], which has a zwit-terionic structure with t/ -bonding of one counterion phenyl ring to Zr, as well as Zr(CH2Ph)3(L)3 and (C5Hj)Ti(CH3)2(L)2 complexes by this method (57). 

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