Hydride complexes of platinum containing phosphine and halostannyl ligands have been known since 1965 [i]. Despite the important role which these compounds play in homogeneous catalysis reactions [2], no reliable data on their structure in solutions are available in the literature. Compounds obtained by the reaction between trans-[HPtCl(PPh3)=] and SnCI2 under different conditions, to which the formula of trans-[PtH(SnCl3)(PPh3)2] has been ascribed, differed in physical properties [i, 3].

The mechanism of hydrogenation of alkynes catalyzed by the [(PR3)(2)PtHX]/SnX2 system (PR3 = PPh3, PMePh2; X = Cl, Br) has been studied by means of parahydrogen-induced polarization of IH spectra (PHIP). Dihydride intermediates confirming the stepwise hydrogenation at room temperature were observed when the reaction was run in acetone. The obtained H-1-PHIP spectra, together with NMR data for related species, are consistent with the formulation of these intermediates as cis-[H2Pt(PR3) (SnX3) (sigma-alkenyl) (acetone)], where the (sigma-alkenyl ligand originates from an insertion reaction of the alkyne (1-phenyl-1-propyne, 1-phenyl-1-butyne, diphenylacetylene, 3,3-dimethylbutyne). At elevated temperatures, the hydrogenation in acetone proceeds as a cis-synchronous transfer of the two hydrogen atoms of parahydrogen to the substrate molecule. A mechanism for this synchronous hydrogenation is suggested.

Rhodium(I) dimeric complexes, [(Ph 3 P) 4 Rh 2 Cl 2 ] and [(C 2 H 4 ) 4 Rh 2 Cl 2 ], form active catalysts for alkenes isomerization on interaction with tertiary phosphine and tin dichloride in CH 2 Cl 2 . Besides 2-methylbut-2-ene, which is the normal product of 1,2-double bond migration, 3-methylbut-1-ene gives the product of unusual 1,3-double bond migration, 2-methylbut-1-ene, which is formed at early stages of the reaction under kinetic control in over-equilibrium quantities. The proposed mechanism for 1,3-double bond migration includes the methyl C−H bond activation, followed by intramolecular transfer hydrogenation.

An interaction of trans -[PtH(SnX 3 )L 2 ] (I, L = PPh 3 , PMePh 2 , PEt 3 ; PBu 3 ; X = Cl, Br) with ethylene, propene and 2-methylpropene has been studied by means of 31 P and 1 H NMR spectroscopy. The reactions of platinum hydrides I with ethylene are rapid and reversible at −90°C, giving cis -[PtR(SnX 3 )L 2 ] (II, R = C 2 H 5 ). The reaction of propene with I (L = PPh 3 , PMePh 2 ) gives II, R = C 3 H 7 . 13 C and 1 H NMR spectra prove the n-propyl structure for II, L = PMePh 2 , X = Cl. Complexes II irreversibly isomerize into trans -[PtR(SnX 3 )L 2 ] between −50° and 0°C. The equilibrium constants and rates are estimated for the reactions of I with alkenes. They decrease as a function of L (PMePh 2 > PPh 3 > PBu 3 > PEt 3 ) and X (Br > Cl). The reactivities of alkenes decrease with increase of steric hindrances at the double bond.

The mechanism of but-1-ene, pent-1-ene and 3-methylbut-1-ene isomerization catalysed with trans-[PtH(SnX3)L2] (I, L = PPh3, PMePh2, PEt3, PPr3; X = Cl, Br) have been studied. Stoichiometric reactions of I with the alkenes proceed even at −90°C giving cis-[Pt(alkyI-1) (SnX3) L2] (II). The equilibrium amounts of II are dependent on the nature of the phosphines, halogens and alkenes. The isomerization rates, determined at +20°C, change in parallel with the relative stabilities of II as a function of phosphine (PMePh2 > PPh3 > PAlk3) and halogen (Br > Cl), and decrease with methyl substitution at γ- and δ- carbons of the alkenes. 2-Substituted alk-1-enes undergo no isomerization in the reactions under investigation. When L is PPh3 or PMePh2, the main platinum-containing species in the course of the isomerization are trans-[Pt(alkyl-1) (SnX3)L2], appearing as a result of cis-trans isomerization of II. The conversion of I, L = PAlk3 into related trans-alkyl complexes, and oxidation of I, proceed more slowly than the isomerization of alkenes. The ratio of cis- to trans-alk-2-enes is dependent on the size of L and is a maximum for L = PPh3.

The authors have shown that the complex (Rh(PPh/sub 3/)/sub 2/SnCl/sub 3/) (I) is an active catalyst for the isomerization of 1-hexene to a mixture of cis- and trans-2-hexenes and cis- and trans-3-hexenes in CH/sub 2/Cl/sub 2/ at 25/sup 0/C in the absence of molecular hydrogen. The addition of gaseous HCl or excess PPh/sub 3/ sharply lowers the catalyst activity. The observed reaction presumably proceeds through a ..pi..-allylhydride mechanism (i.e., though the ((eta/sup 3/-allyl)RhH(PPh/sub 3/)/sub 2/SnCl/sub 3/) intermediate). This is indicated by 1,3 deuterium migration leading to a random deuterium distribution between C/sup 1/ and C/sup 3/ in 3-propene-D/sub 1/ upon its reaction with (I) in CH/sub 2/Cl/sub 2/ studied using /sup 13/C NMR spectroscopy.

Literature data and results obtained on the mechanisms of olefin hydrogenation and isomerisation using platinum and rhodium complexes, in particular, with PtSn and RhSn bonds were analysed. The role of alkyl derivatives of platinum and rhodium in these reactions is discussed.

The hydridotrichlorostannyl rhodium complex [HRh(SnCl3)5]3− reacts with tributylphosphine in organic solvents to give, depending on the P∶Rh ratio, mono- and diphosphine hydrido complexes of RhIII, together with the complex [RhISnCl3)3 (Bu3P)2]2−, the composition of the reaction mixture depending on the solvent.

The 2(1)-bromopropyl tosylates are not isomerized via the 1,2-migration of bromine under the conditions of isomerizing the bromoacetoxypropanes. Three possible mechanisms of the indicated rearrangement are discussed: acylonium (a) and via the ionization of either the C-O bond (b) or the O-Br bond (c) in the initial reaction step. Mechanism b was rejected on the basis of the experimental data.

New rhodium hydride complexes with general formula [R4N]3[HRh(SnCl3)5] were synthesized.