Alkyl, aryl, alkene and alkyne complexes

Methods of forming carbonyl halides include starting from binary metal carbonyls (equations 24.57-24.59) or metal halides (equations 24.65-24.67). 

The product of reaction 24.68 is a useful precursor to Ru(PPh3)3(CO)2 (equation 24.69). This 18-electron complex readily loses one PPh3 ligand to give an unsaturated Ru centre to which H2, R2C=CR2, RC=CR and related molecules easily add. 

The 16-electron halide complexes cw-[Rh(CO)2l2] and tra w-[Ir(CO)Cl(PPh3)2] (Vaska s compound) undergo many oxidative addition reactions and have important catalytic applications (see Chapter 27). The product of reaction 24.67 is a catalyst precursor for alkene hydrogenation. Vaska s compound readily takes up O2 to give the peroxo complex 24.54. 

---

Chapter 23 Alkyl, aryl, alkene and alkyne complexes 725... 

An earlier review treated the organometallic derivatives, including alkyl, aryl, vinyl, alkynyl, carbonyl, carbene, alkene and alkyne complexes,16 and these will not be treated here (see Table 1 for other books and reviews on organogold chemistry). Two important articles dealing with [AuCl(CO)], including its structure and catalytic properties, have been published recently.97,381... 

Indenyl)rhodium(I) complexes, preparation, 7, 184—185 Indium complexes acid halide reactions, 9, 683 in alkene and alkyne allyindations, 9, 693 alkyl, aryl, alkynyls, 3, 288 in alkynylations, 9, 720... 

Addition reactions of three kinds of main group metal compounds, namely R—M X (carbometallation, when R are alkyl, alkenyl, aryl or allyl groups), H—M X (hydrometallation with metal hydrides) and R—M —M"—R (dimetallation with dimetal compounds) to alkenes and alkynes, are important synthetic routes to useful organometallic compounds. Some reactions proceed without a catalyst, but many are catalysed by transition metal complexes. 

Hydride complexes of palladium and platinum are almost invariably stabilized by phosphine ligands and play an important role in catalytic processes such as hydrogenation. Examples are Pt(H)ClL2 and Pt(H)2L2, as well as hydrido alkyls and aryls, trans,-Pt(H)(R)L2. There are cis and trans isomers. A typical reaction is the insertion of alkenes and alkynes into the Pt—H bond 33... 

The alkene, allyl, and alkyne complexes of Pd and Pt have been discussed to a large extent in earlier Sections, as have the use of palladium species in catalysis (Chapters 23 and 24). Here we deal mainly with complexes of the type MXHL2 and MXRL2 where X is halogen, R is an alkyl or aryl group and L is usually a tertiary phosphine. 

The reactivity of the C—Pd bond is very diverse. In addition to the previously discussed j8-elimination and reductive elimination, alkyl-, benzyl-, aryl-, alkenyl-, and alkynyl-Pd complexes can undergo syn addition of the C—Pd bond across the C—C bond of alkenes and alkynes, that is, carbopalladation. This reaction can generate alkyl- or alkenyl-Pd complexes and is occasionally used as a preparative method, as exemplified in Scheme 31.Closely related is the hydropalladation of alkenes and alkynes. However, these processes are mostly observed under catalytic conditions. 

The first X-ray structure of a zirconocene(II)—alkene complex, zir-conocene(II)-stilbene stabilized by phosphine, was reported by Takahashi and coworkers [7]. Basically, the formation of zirconocene alkene or alkyne complexes may be achieved in three different ways (a) by a reductive elimination process starting from alkyl, alkenyl or aryl zirconocene(lV) complexes (Eq. 1, and Eqs. 5-6) [1-5,8,9], or (b) by ligand exchange reactions involving carbonyl or phosphine complexes (Eq. 7), or (c) by -C-C bond cleavage of zircona-cyclopentanes or zirconacyclopentenes (Eqs. 8-9) [10,11]. 

---