Synthesis, reactions and multinuclear NMR spectroscopic studies of organo bimetallic and trimetallic compounds

Mampa, Richard Mokome
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The 207Pb and 119Sn NMR chemical shift were used to study the effect of temperature on Ph3MCl (M= Pb and Sn) adducts in the presence of 10% excess pyridine. The 207Pb and 119Sn chemical shift indicate a slow exchange at low temperatures below -90 0C and a significant exchange at higher temperatures above 10 0C. A plot of temperature against 207Pb or 119Sn chemical shift showed a curve with gentle slope at lower and a steep slope at higher temperatures. A good linear correlation (coefficient. of 0.95) between Hammett substituent constant and 207Pb or 119Sn chemical shift of para-substituted derivatives of* (py* = NMe2, OMe, Me, Ph, H, Br, COPh and COMe; at -90 0C in CD2Cl2/CH2Cl2) was found. Both 207Pb and 119Sn chemical shift ranges are characteristic of five coordinate systems resolving into trigonal bipyramidal geometry as shown by X-ray crystal structures. New complexes of the type [CpFe(CO)(SnPh3)L] (L = PPh3, PBu3, PCy3, PMe3, P(NMe2)3, PMePh2, PMe2Ph, P(p-FC6H5)3, P(p-OMeC6H4)3, P(p-tolyl)3, P(OMe)3, and P(OPh)3 were synthesized by ultraviolet irradiation of [CpFe(CO)2(SnPh3)] and the appropriate phosphine or phosphite ligand. 57Fe NMR studies of the complexes showed an increasing linear relationship with Tolman’s steric parameter, whereas with Tolman’s electronic parameter the 57Fe chemical shift showed a decrease. The X-ray crystallographic profile of the selected new piano stool type complexes shows a significant correlation to the NMR data (solution state), i.e. Fe-Sn, Fe-P bond length and Sn-Fe-P bond angle against chemical shifts of 207Pb and 119Sn. Disubstituted complexes of the type [CpFe(SnPh3)L2] (L = PMe3, PMe2Ph, P(OMe)3 and P(OPh)3 were synthesized under similar conditions as monosubstituted compounds. The correlation trends between the NMR data and X-ray crystallographic profiles are similar to those found for monocarbonylated complexes. Tungsten phosphine complexes of the type [W(CO)5(PR3)] (prepared from [W(CO)6] under thermal conditions) and [W(CO)4(NCMe)(PR3)] (prepared from [W(CO)5(PR3)] by use of Me3NO-promoted decarbonylation) were synthesized and characterized by, among other methods X-ray diffraction techniques (R = Ph, p-tolyl, p-OMeC6H4, p-FC6H4, p-CF3C6H4, and NMe2). The tungsten complexes [W(CO)4(NCMe)(PR3)] react with [(dppp)Pt{C≡C-C5H4N}2] at room temperature to form new complexes of the type [(dppe)Pt{C≡C-C5H4N-W(CO)4(PR3)}2] which were characterized unambiguously by NMR spectroscopy. There is a fair correlation between 195Pt and 183W NMR chemical shifts and Tolman’s electronic parameter which indicates a fair influence by the substituents of the phosphorus atom on both metal centres. Tungsten complexes of the type [W(CO)4(NCMe)(L)] (L= PPh3, P(p-FC6H4)3, P(p-OMeC6H4)3, P(p-tolyl)3, P(p-CF3C6H4)3, PMePh2, and PPh2(C6F5) react with [(PPh3)2Rh(H)2(pytca)] (pytca = 2-(4-pyridyl)thiazole-4-carboxylate) to form new complexes of the type [(PPh3)2Rh(H)2(pytca)- W(CO)4(L)] under mild conditions. These complexes were characterized principally by NMR spectroscopy and X-Ray crystallography (L = P(p-tolyl)3). Crystallographic evidence was found for π-π-π interactions involving two phenyl rings, one of the two phosphines bonded to rhodium atom, one of the three phosphines bonded to tungsten and the pyridyl ring of the thiazole corboxylate group. A second π-π interaction is found between a thiazole and a phenyl ring of the phosphine ligand bonded to the rhodium atom. A fair correlation was found between the rhodium and tungsten chemical shift measured from this series of complexes as a result of varied paraphenyl substituent of phosphine ligand bonded to the tungsten atom. This therefore implies the possible existence of electronic communication between the two bridged metal centres.