Vibrational spectra of intra- and inter-metal and semimetal bonds

Linear carboxylic acid esters from .alpha. olefins. 2. Catalysis by homogeneous palladium complexes

“…In contrast to analogous platinum bimetallic catalysts,1 [(C6H5)3P]2PdCl2-SnCl2 carbonylates at least three classes of polysubstituted olefins (expt [26][27][28][29][30][31][32][33]. Sterically hindered branched a olefins in which the alkyl substituent is on the ß or 7 carbon provide excellent examples of regioselective carbonylation.…”

“…containing more than two SnCl3~c oordinated to each palladium. 31 Although unequivocal identification of the active catalyst has not been possible, evidence, such as the suppression of the rate by excess triphenylphosphine, and additional tin(II) chloride, suggests several interdependent equilibria existing in these tin-rich solutions (eq 5) prior to car-…”

Linear carboxylic acid esters from .alpha.-olefins. I. Catalysis by homogeneous platinum complexes

“…Dichlorobis(triphenylarsine)platinum(II), in the absence of a Group 4B metal halide cocatalyst, fails to carbonylate a olefins (Table II, expt 20). Significant yields of methyl octanoate are afforded, however, with metal chloride cocatalysts such as tin(II) chloride, tin(IV) chloride, and lead(II) chloride; the highest yields of linear ester are obtained with tin(II) chloride (expt 14) at Sn:Pt mole ratios of around 10 (expt 14, [22][23][24]. Similarly, among different tin(II) halides, SnCl2 is more effective than Snl2.…”

“…This order of effectiveness (eq 4 and 5) parallels that found for the bimetallic hydroformylation catalysts (R3P)2PtX2-MX222, and the order of stability of platinum-Group 4B metal bonds. [23][24] It should be noted, nevertheless, that no carbonylation is evident when SnCls-is replaced by other powerful x-acceptor ligands25-26 such as antimony trichloride, cyanide ion, and CO itself. For the more active platinum catalysts, the principal side reactions are (a) the formation of small quantities of branched ( -methyl) acid esters, in this case methyl 2methylheptanoate, and (b) isomerization of the 1-heptene to internal isomers, notably cisand trtms-2-heptene.…”

“…It may be noted that analogues of the hydridoplatinum species A and B have been prepared previously,20•35 as have phosphine-stabilized platinum-alkyl complexes36•37 and platinum-acyl species analogous to F, under more forcing conditions. 30 Intermediate platinum carbonyls such as Pt(CO) (EtOH) (PPh3)2(SnCl3)2 have also been isolated by the carbonylation of phosphine treated platinum-tin solutions.38 However, while maximum catalyst activity is realized in this work at Sn:Pt mole ratios of about 10 (expt 14, [22][23][24], no Pt-Sn complexes with Group 5B ligands have been isolated having more than two SnCl3_ ions per plati- num.24 As in related catalysis,33 it is likely that several interdependent equilibria exist prior to carbonylation, with at least partial displacement of the organoarsine ligand being consistent with (a) the relatively low sensitivity of the isomer distribution (selectivity 90-98 mol %) to significant changes in Group 5B ligand structure (Table I) and (b) the slower carbonylation rate in the presence of excess organoarsine (expt 4). Mixed complexes such as (PhaAs^PtCKSnCls) are known,39 although SnCla may be readily displaced by other strong back-bonding ligands24 such as CO.…”