Metals in organic syntheses VII. The isolation of trans-[Pt(COPr-n)Cl(PPh3)2] (I) and trans-[Pt(SnCl3)(COPr-n)(PPh3)2] (II), active intermediates in the hydroformylation of propene catalyzed by a [PtCl2(PPh3)2]-SnCl2 precursor. The crystal and molecular structure of complex I and a comparison with its palladium analog.

Trans-[PtCl(COPr-n)(PPh3)2] (I) has been isolated in good yield from the mixtures obtained by treating a mixture of propene, cis-[PtCl2(PPh3)2] and SnCl2•H2O with carbon monoxide in the presence or absence of hydrogen in an alcohol in which no significant hydroformylation or hydroxycarboalkylation actually occurs. The cis-[PtCl2 (PPh32]-SnCl2•2 H2O system is highly active in the catalytic hydroformylation in methyl isobutyl ketone, and from reaction mixtures in this medium trans-[Pt(SnCl3)(COPr-n)(PPh3)2] (II) has been isolated (33% yield). The presence of a Pt-Sn bond in a complex of type II plays a key role in promoting the formation of the aldehyde from the acyl derivative, but it is not necessary for the formation of intermediate I, since this can be isolated in good yield even in the absence of the tin compound. The higher regioselectivity observed using intermediate I or II, compared with that when the precursor is used is discussed in terms of steric effects of the ligands competing for coordination to the platinum atom. The catalytic properties of complex I are compared also with those of its palladium analog, which catalyzes only the hydrocarboalkoxylation but does this even in the absence of SnCl2. The crystal and molecular structures of the title complex I and its palladium analogue have been determined from three dimensional X-ray diffractometer data. Both complexes are isostructural and crystallize in the monoclinic space group P21/n. Cell parameters are as follows: [PtCl(COPr-n)(PPh3)2], (I), a =13.266(8), b =24.029(10), c =12.142(8) Å, beta =115.4(1)°, Z =4; [PdCl(COPr-n)(PPh3)2], (III), a=13.292(8), b =23.800(10), c =12.196(8) Å, beta=115.2(1)°, Z =4. Full-matrix least-squares refinement converged at R =0.048 (I) and R =0.054 (III). The structures have approximately square-planar geometry and the dimensions are not unusual.