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The correlation between structure and bonding, and the reactivity patterns of η3-allylmetal complexes is discussed. Emphasis was laid on the reactions which have a strong bearing on homogeneous catalysis involving group 10 metal complexes. The reactions surveyed here include; the generation and cleavage (nucleophilic substitution, and reductive elimination) of η3-allyl complexes, dynamic equilibria, and electrophilic substitution of η1-allyl complexes.

Relative olefin coordination ability in Pt(η3-CH2CMeCH2)(CH2=CHC6H4Y)(C6F5)(2)was determined to show the stability trend unusually weakly dependent on the electronic property of the substituent Y. The crystal structure of the styrene complex 2 (Y= H) revealed the C=C bond oriented parallel to the coordination plane. The nature of Pt-olefin bond in 2 has been discussed in terms of these stability and structural trends.

Molecular level understanding of a relationship between structure, bonding and reactivity of olefin and allyl complexes of group 10 metals is presented. In addition to three types of olefin complexes previously known, namely 3-coordinated M (O), 4-and 5-coordinated M (II) complexes, a complex containing, π-olefin and, π-allyl ligands simultaneously represents a new type of the group 10 metal-olefin compounds possessing some unique stability, structural and reactivity aspects. Dynamic equilibria and electrophilic substitution of novel σ-allyl-metal complexes are presented. Mechanistic knowledge concerning stoichiometric reactions of π-allyl-metal complexes, namely nucleophilic substitution and reductive elimination, is surveyed and its relevance to actual catalysis is also discussed.

The reaction of alkyl, aryl and vinylthallium(III)_diacetates with nitronate ions gives moderate to good yields of the carboncarbon bonded products. The reaction of the alkyl and arylthallium(III) analogs proceeds through radical intermediates which are generated by electron-transfer activation of the thalliumcarbon bond.

This survey will deal with 1) reviews, 2) synthesis, structure and spectroscopy of organothallium(III) compounds, 3) compounds containing thallium-metal bonds, 4) reactions of organothallium(III) compounds and 5) thallium(I) compounds.

Some new methylethylthallium derivatives, as well as several dimethylthallium and diethylthallium compounds, were prepared. The compounds, CH 3 (C 2 H 5 )TIX where X = SCH 3 , SC 6 H 5 , oxinate and tropolonate were found to redistribute into (CH 3 ) 2 TIX and (C 2 H 5 ) 2 TIX at room temperature and/or at higher temperatures. The reverse reaction between (CH 3 ) 2 TIX and (C 2 H 5 ) 2 TIX where X = SCH 3 , SC 6 H 5 , oxinate, tropolonate and salicylaldehydate also took place with considerable ease, yielding the corresponding methylethylthallium derivative.

Various mixed diorganothallium isobutyrates were prepared. A novel replacement reaction was observed by treating them with tetramethyltin in methanol as follows, where R′ is evidently limited to groups in which the carbon atom bonded to thallium has sp Or sp 2 hybridization. We have briefly reported the preparation of mixed diorganothallium(III) chlorides by the reaction of monoorganothallium diisobutyrates with tetramethyltin or phenylboronic acid, followed by addition of hydrochloric acid. similar reactions are found to proceed smoothly and nearly quantitatively as shown in eqns. (1) and (2). We have also found that monomethylthallium diisobutyrate reacts with other tetraalkyltins. The reaction with either tetraethyl- or tetra-n-propyltin was slow, and the product was contaminated by a dimethylthallium species. It is not yet clear whether this species was formed from the disproportionation of CH 3 TlY 2 or CH 3 RTlY. However, with the exception of these two cases, the alkylation reaction proceeds straightforwardly as shown in (1) and (1′). This is noteworthy in view of the report 3 that phenylthallium dichloride reacts with alkyl Grignard reagents to give a mixture of diphenylthallium halide and the corresponding dialkylthallium halide. Tetramethyltin also reacts with various mixed diorganothallium isobutyrates, causing a novel replacement reaction as shown in eqn. (3) This reaction proceeds smoothly, and methanol is thought to act as a proton source for the formation of the hydrocarbons (R′H). It should be noted that methylethylthallium isobutyrate does not undergo this reaction, i.e. the organic group (R′) is replaced only when the carbon atom bonded to thallium has sp or sp 2 hybridization. Presumably this reaction does not proceed by way of a simple R′-methyl exchange mechanism. In that event the reaction of R(C 6 H 5 )TlY with (CH 3 ) 4 Sn would give the intermediate (CH 3 ) 3 (C 6 H 5 )Sn, but this compound is found to be unreactive toward methanol under the reaction conditions employed. A likely mechanism may involve isobutyryloxy-methyl exchange, and the resulting CH 3 RR′Tl could then react with methanol to lose only the most electronegative R′ group, preferentially forming R′H before the disproportionation of CH 3 RR′Tl takes place. However, such a disproportionation reaction through intermolecular exchange of alkyl groups has been reported to occur very rapidly in mixed tri(methyl, ethyl)thallium and tri(methyl, vinyl)thallium systems4. Alternatively, it is also possible that the methylation by tetramethyltin and the cleavage of the TI-R′ bond take place simultaneously in the sense of a concerted mechanism, without formation of a CH 3 -RRTl intermediate.

Several dimethylthallium derivatives were studied by means of a study of their IR and NMR spectra and by measurements of their physical properties. These new compounds, (CH3)2· TlSC6H5, (CH3)2TlOC6H4Cl-o, and (CH3)2Tl[B(C6H5)], are described. By correlation with earlier reports, it is possible to classify dimethylthallium derivatives into two groups according to the nature of the hybridization of the Tl-bonding orbitals. The experimental results can be interpreted in a straightforward and consistent manner.

In o r d e r to s t u d y the c o n f i g u r a t i o n and the n a t u r e o f bond ing o f d i m e t h y l t h a l l i u m a c e t y l a c e t o n a t e , we have examined the NMR and i n f r a r e d s p e c t r a o f t h i s compound. The i n f r a r e d spec t rum of (CH3)2Tl(acac) in c h l o r o f o r m (Table 1) shows the p r e s e n c e o f bands a s s o c i a t e d wi th bo th t he symmetr ic and a n t i s y m m e t r i c T1-C s t r e t c h i n g v i b r a t i o n s a t 482 cm °1 and 566 cm °1 , r e s p e c t i v e l y . Th is s u g g e s t s t h a t t he d i m e t h y l t h a l l i u m group shou ld have a n o n l i n e a r c o n f i g u r a t i o n i n c h l o r o f o r m . Other f e a t u r e s o f the i n f r a r e d spec t rum a r e s i m i l a r to t h o s e (1) o f known c h e l a t e d me ta l a c e t y l a c e t o n a t e s . NMR d a t a a r e g iven in Table 2. For compar i son , NMR d a t a f o r d i m e t h y l t h a l l i u m o x i n a t e which has been r e p o r t e d (2) to have a c h e l a t e d s t r u c t u r e in c h l o r o f o r m by the s tudy o f the e l e c t r o n i c s p e c t r a a r e i n c l u d e d i n the t a b l e . In c h l o r o f o r m , the ~ v a l u e s o f the y and methyl p r o t o n s o f the a c e t y l a c e t o n a t e group in (CH3)2Tl(acac) a r e a t a h i g h e r magne t i c f i e l d t han t h o s e (3 ,4) found in t i n ( I V ) a c e t y l a c e t o n a t e s , w h i l e in Tab le 1 i t i s seen t h a t the C=0 s t r e t c h i n g f r equency i s h i g h e r and the M-0 s t r e t c h i n g f r e q u e n c y i s lower than t h o s e (5 ,6) in t i n ( I V ) a c e t y l a c e t o n a t e s , r e s p e c t i v e l y . This c o r r e l a t i o n between t h e r e s u l t s o f the NMR and the i n f r a r e d s p e c t r a has been e s t a b l i s h e d p r e v i o u s l y ( 3 ) f o r t i n ( I V ) a c e t y l a c e t o n a t e s . Thus our r e s u l t s i n d i c a t e t h a t the a c e t y l a c e t o n a t e l i g a n d i s r a t h e r weak ly c h e l a t e d to the d i m e t h y l t h a l l i u m moie ty in c h l o r o f o r m s o l u t i o n .

Several methyl(allyl)thallium derivatives have been prepared for the first time. The IR and PMR spectra of these compounds indicate the presence of σ-allylthallium bonds. In the cleavage reactions of these compounds with tetramethyltin in methanol or with metal salts such as Hg(OCOCH3)2, PdX2 (X  OCOC2H5 and Cl) and RhCl3·3H2O, preferential cleavage of the allylthallium bond occurs to give propylene in the case of tetramethyltin and allylic derivatives of the metals in the other cases.

Seven new alkyl(cyano)thallium derivatives have been synthesized. The observed linear relation between ν(Tl-CN) and ν(CN) frequencies in these compounds could be interpreted in terms of the strength of Tl-ligand interaction.

Several monomethyl- and monoethylthallium derivatives have been synthesized for the first time. Methylthallium dicarboxylates are found to decompose when heated or treated with halide anions to give thallous ion and methyl esters of carboxylic acids, methanol or methyl halides. From the structural studies on RTl(Ox)2 and RTl(OOCC3H7-iso)2 (R = CH3 and C2H5) in solution, it is suggested that these compounds have penta-coordinated thallium atoms.

Some trimethylsilylmethyl derivatives of thallium(III) have higher stability and unusual coordination behavior in comparison with simple alkylthallim(III) analogs for steric reasons.

Synthesis of some new trimethylsilylmethyl, neopentyl, and isobutylthallium compounds is described. Dialkykhallium halides containing these bulky alkyl substituents were found to be dimeric, in marked contrast to the polymeric dimethylthallium halide analogs. Trimethylsilylmethylthallium diisobutyrate possesses much higher stability than the methyl and ethylthallium analogs. These facts were discussed in terms of the steric bulk of the alkyl groups attached to thallium.

Allyloxycarbonyl complexes of Pt II undergo ready decarboxylation to give the corresponding π-allylplatinum(II) complexes. The importance of olefin coordination to a platinum atom in the transition state is suggested.

Methyl- or ethyl(cyano)thallium acetate has been prepared by using a methyltin or ethyltin compound, such as (CH 3 ) 2 SnF 2 , (CH 3 ) 3 SnOAc, (CH 3 ) 4 Sn or (C 2 H 5 ) 4 Sn, together with thallic acetate and sodium cyanide. The reactions of some methyltin derivatives with thallic acetate in the absence of cyanide anion have also been investigated.

η1-Allyl(aryl)palladium complexes react with some electrophiles to result in the selective Pd-allyl bond cleavage with 1,3-transposition, while the corresponding η3-allyl(aryl)palladiums and the electrophiles give rise to the selective Pd-Ar bond cleavage. The η1-allyl complexes also react with CCl4 and CHCl3 under very mild conditions to give good yields of CH2=CHCHR(CR′Cl2) (R= H, Me; R′= Cl, H).

Molecular level understanding of a relationship between structure, bonding and reactivity of olefin and allyl complexes of group 10 metals is presented. In addition to three types of olefin complexes previously known, namely 3-coordinated M (O), 4-and 5-coordinated M (II) complexes, a complex containing, π-olefin and, π-allyl ligands simultaneously represents a new type of the group 10 metal-olefin compounds possessing some unique stability, structural and reactivity aspects. Dynamic equilibria and electrophilic substitution of novel σ-allyl-metal complexes are presented. Mechanistic knowledge concerning stoichiometric reactions of π-allyl-metal complexes, namely nucleophilic substitution and reductive elimination, is surveyed and its relevance to actual catalysis is also discussed.

Allyloxycarbonylplatinum(II) complexes readily afforded π-allylplatinum(II) complexes by decarboxylation under several reaction conditions. The importance of olefin coordination to a platinum atom in the transition state is suggested. The other novel routes to π-allylplatinum(II) complexes which apparently involve a similar reaction intermediate are also described.

Hydrogen-1 n.m.r. conformational analyses of some stabilised oxythallation products from styrene, o-allylphenol propylene, and oct-1-ene have been performed primarily on the basis of the variation in thallium–proton spin–spin couplingconstants. The results have been applied to the oxythallated adduct of trans-β-deuteriostyrene to provide the first direct evidence for trans addition in the oxythallation of acyclic olefins.

Reactions of organothallium compounds, RT1X2 with electron donors are surveyed. Interaction of the donors with RT1X2 provides the T1-C bond with the enhanced reactivity compared with that of the original RT1X2 or with the reactivity pattern not found in the original These include homolysis of the T1-C bond, enhanced electrophilic attack at the thallium-bound R group, and enhanced nucleophilic substitution at the thallium-bound aryl and vinyl groups. The relevant examples of these trends are described in the reactions employing, as the donors Me2CNO2 −, N-benzyl-1,4-dihydronicotinamide, CuX, PR3, I−, NaBH4 and hydrazine. Relevance of the reductive activation of RT1X2 as well as related RHgX and RPbX3 in organic synthesis is discussed.