Giuseppe Cardaci

Solution structure investigations of olefin Pd(II) and Pt(II) complex ion pairs bearing α-diimine ligands by 19F, 1H-HOESY NMR

Complexes [M(η1,η2-C8H12OMe)((2,6-(R)2C6H3)NC(R′)C(R′)N((2,6-(R)2C6H3))]PF6 (where M=Pd, R=H and R′2=Me2 (1), M=Pd, R=Me and R′2=Me2 (2), M=Pd, R=Et and R′2=Me2 (3), M=Pd, R=iPr and R′2=Me2 (4), M=Pd, R=iPr and R′2=An (5), M=Pt, R=iPr and R′2=An (6)) were synthesized by the reaction of [M(η1,η2-C8H12OMe)Cl]2 with the appropriate α-diimine ligand in the presence of NH4PF6. Their ion pair structure in solution was investigated by detecting dipolar interactions between protons belonging to the cation and fluorine nuclei of the anion (interionic contacts) in the 19F, 1H-HOESY NMR spectra. In complexes 1–4, the anion in solution is located close to the peripheral protons of the α-diimine ligand and it interacts with the R′ protons and with the R protons that point toward the R′ groups. The steric protection of apical position exerted by the R substituents is clearly illustrated by the absence of interionic contacts between any protons of the cycloctenylmethoxy-moiety and the anion for R≥Me in 1–4. In complexes 5 and 6 the interactions between the anion and the peripheral N,N protons also predominate but other anion–cation orientations are significantly present and, consequently, the interionic structure is less specific.

The mechanism of substitution of π-(PhCHCHCOR)Fe(CO)3 complexes with PPh3, AsPh3 and SbPh3

Abstract The reaction between π-(PhCHCHCOR)Fe(CO) 3 (R = H, CH 3 , Ph) and L (L = PPh 3 , AsPh 3 , SbPh 3 ) in acetone occurs in two steps. The products of the first step are the π-(PhCHCHCOR)Fe(CO) 3 L complexes, which in the second step yield Fe(CO) 3 L 2 and π-(PhCHCHCOR)Fe(CO) 2 L. The kinetic results indicate that the first step is association of the substrate with the ligand. The variation of the ratio [Fe(CO) 3 L 2 ]/[π-(PhCHCHCOR)Fe(CO) 2 L] with L suggests three different reaction paths for the second step.

Vibrational spectra of π-allyl-and π-allyl-d5-dicarbonyl-nitrosyliron

Abstract Vibrational spectra of π-C3H5Fe(CO)2NO and π-C3D5Fe(CO)2NO have been studied in the liquid and solid states. The spectra have been interpreted on the basis of a C3 molecular symmetry. A reassignment of some bands is proposed for the allylic fragment based on vH/vD isotopic shifts. Examination of spectra of deuteriated derivatives has also allowed a reasonable assignment of all modes involving the FeCO and FeNO groups.

Dipole moments and internal rotation in 1,1′-dihaloferrocenes

Abstract The dipole moments of bromoferrocene, iodoferrocene, 1,1′-dibromoferrocene and 1,1′-diiodoferrocene have been measured in benzene. They indicate that the potential barrier between the cis and trans forms, which is very small for 1,1′-dichloroferrocene, increases for 1,1′-dibromo- and 1,1′-diiodoferrocene. The potential energy function shows minima at 36°, 108° and 180°. The differences ΔE1 = E36 − E180 for the series have been calculated on the assumption that the minima at 180° and 108° are equal. The values obtained are consistent with increasing steric hindrance in the series Cl, Br, I.

Polarographic behaviour of π-allylic complexes of transition metals I. π-allylic dicarbonylnitrosyliron complexes

The polarographic behaviour of π-C3H5Fe(CO)2NO, π-(1-CH3C3H4)Fe(CO)2NO, π-(2-CH3C3H4)Fe(CO)2NO, π-(1-ClC3H4)Fe(CO)2NO, π-(2-ClC3H4)Fe(CO)2NO and (2-BrC3H4)Fe(CO)2NO have been investigated in CH3CN. Chemical (with NaBH4) and electrochemical reductions, carried out on some of the above complexes have both been shown to follow the same pathway. On the basis of the results obtained a general reduction mechanism is proposed and discussed. Effects of substituents on the mechanism and on the halfwave potentials has also been examined.

Kinetics of monosubstitution reactions of phosphane-, arsine- and stibine-ligands with CO(CO)3NO.

Abstract The kinetics of the ligand substitution reactions between Co(CO) 3 NO and P(C 6 H 5 ) 3 As(C 6 H 5 ) 3 ,Sb(C 6 H 5 3 1,2 bis(diphenylphosphino)ethane has been studied. For the first three ligands it was found active a kinetic two term rate law for the monosubstitution reaction of the type v = (k 1 + k′[L]) [Co(CO) 3 NO], coming from a comaparable contribution of a first- and a second-order path. There is evidence, also from activation enthalphy and entropy data, that the first-order path be a dis sociative one; the k 1 values for all three ligands are almost coincident in a reasonably wide range of temperature. The second-order path is assigned as an associative one, the value of its overall rate constant k′ being affected by ligand variation in the order P(C 6 H 5 ) 2 CH 2 CH 2 P(C 6 H 5 ) 2 > P(C 6 H 5 ) 3 »As(C 6 H 5 ) 3 .Sb(C 6 H 5 ) 3 consequently, the relative contribution of the first-order path to the overall reaction rate increases for the last three ligands in the reversed order, mean figures for a ligand concertration of 10 −1 M being 0.8, 36 and 85% resp. with P(C 6 H 5 ) 3 and Sb(C 6 H 5 ) 3 . Such a behaviour has been interpreted as a function of the basicity. π-acceptor ability and polarizability of the ligands concerned, the first two factors appearing in these cases to prevail. Also the first-order chelation process with 1,2-bis(diphenylphosphino)ethane, following monosustitution, appears from thermal data to be an associative one.

Preparation of methyl hydride and dimethyl complexes of osmium and iron: reaction of M(CO)2(PMe3)2CH3I and [M(CO)3(PMe3)2CH3]+BPh4− (M=Os, Fe) with borohydrides and lithium methyl

Abstract cis,trans- Os(CO) 2 (PMe 3 ) 2 CH 3 I ( 1 ) and fac -[Os(CO) 3 (PMe 3 ) 2 CH 3 ] + BPh 4 − ( 3 ) react with borohydrides (NaBH 4 , NBu 4 BH 4 , LiBEt 3 H) in diethyl ether to form the methyl hydride complex Os(CO) 2 (PMe 3 ) 2 (CH 3 )H ( 7 ). Similarly the monosubstituted fac- Os(CO) 3 (PMe 3 )CH 3 I ( 9 ) reacts with borohydrides to give fac -Os(CO) 3 (PMe 3 )(CH 3 )H ( 10 ). The isoelectronic complexes of iron cis,trans- Fe(CO) 2 (PMe 3 ) 2 CH 3 I ( 2 ) and fac- [Fe(CO) 3 (PMe 3 ) 2 CH 3 ]BPh 4 ( 4 ) give instead the dihydride complex cis,trans- Fe(CO) 2 (PMe 3 ) 2 H 2 ( 8 ). Complexes ( 1 )–( 4 ) react with lithium methyl to form the dimethyl complexes cis,trans- M(CO) 2 (PMe 3 ) 2 (CH 3 ) 2 [M=Os ( 5 ), Fe ( 6 )]. The structures of the complexes are studied by IR and 1 H-, 13 C{ 1 H}-, 31 P{ 1 H}-NMR spectroscopies. The different results are explained on the basis of a fast reductive elimination reaction in the case of iron and a fast decarbonylation reaction in the case of osmium.

Carbonylation reaction of alkyl complexes of iron and molecular structure of cis,trans-[Fe(CO)2(PMe3)2(CH3)I] and trans,trans-[Fe(CO)2(PMe3)2(CH3)I]

Abstract The carbonylation reaction of cis,trans [Fe(CO) 2 (PMe 3 ) 2 (CH 3 )I] ( Mc ) to cis,trans -[Fe(CO) 2 (PMe 3 ) 2 (COCH 3 )I] ( Ac ) and the isomerization of Ac to trans,trans -[Fe(CO) 2 (PMe 3 ) 2 (COCH 3 )I] ( At ) were studied in polar and apolar solvents. The results suggest that the first step of the carbonylation is the formation of the ionic intermediate [Fe(CO) 3 (PMe 3 ) 2 (CH 3 )]I ( Im ); complexes Ac and At are both formed from the intermediate In at different rates due to the differential cooperative effect of the anion. Further information was obtained by a structural study of complexes Mc and trans,trans -[Fe(CO) 2 (PMe 3 ) 2 (CH 3 )I] ( Mt ), using single crystal X-ray diffraction. The structure models were refined to R = 0.034 for 2270 independent reflections for Mc and R = 0.056 for 2381 independent reflections for Mt. Crystal data: monoclinic, space group P 2 1 / c for both molecules: a = 13.656(2), b = 9.032(3), c = 13.880(6) A , β = 106.78(3)° for Mc ; a = 13.818(3), b = 8.957(2), c = 13.826(3) A , β = 105.21(3)° for Mt. Both complexes present octahedral coordination of the ligands around the metal centre.

Polarographic behaviour of π-allylic complexes of transition metals : II. π-allyltricarbonylcobalt and some phosphinic derivatives

Abstract The polarographic reduction in acetonitrile (ACN) of π-C3H5Co(CO)3 and of the phosphinic derivatives π-C3H5Co(CO)2L [L = P(OC6H5)3, P(OCH2)3CC2H5, P(C6H5)3, P(OC2H5)3, P-n-Bu3, P(C6H11)3] is reported and the reduction mechanism is discussed. The dependence of the E 1 2 of thecomplexes on the properties of the ligands is analysed, and a linear plot of E 1 2 vs. ΔHNP of the ligands is observed. The pseudo first-order rate constants for the reduction of the complexes with NaBH4 in ACN are reported.

The kinetics of the monosubstitution reactions between phosphines and allyldicarbonylnitrosyliron

Abstract The complexes [Fe(CO)(NO)(C3H5(ligand)] (C3H5allyl) have been prepared by treatment of Fe(CO)2(NO)C3H5 with the following ligands : P(n-C4H9)3, P(OCH3)3, P(OC2H5)3. P(OC4H9)3, P[OCH(CH3)32]3CCH3, P(C6H5)2Cl, P(OC6H5)3 and P(C6H5)2CH2CH2P(C6H5)2. The kinetics of these monosubstitution reactions have been examined, and indicate that they proceed through association between starting complex and the ligand. No reaction occurs with pyridine, and the reactions with As(C6H5)3 is slow. The resultsare consistent with the substrate being a class b or soft metal. The rates are little affected by change in dielectric constant or coordinating ability of the solvent. For nucleophites with the same ligand atom (phosphorus) the rates do not depend primarily on the basicity or polarizability of the reagents, but rather on their bulk.