Maria Grassi

Synthesis, X-ray structure and reactivity of cyclopalladated complexes of hydrazones of 1H-indole-3-carboxaldehyde

Abstract By reaction of Li 2 [PdCl 4 ] with substituted hydrazones of 1 H -indole-3-carboxaldehyde the corresponding cyclopalladated complexes have been isolated and characterized. Compound 1a [C 11 H 10 ClN 3 OPd] reacts with PPh 3 by halogen displacement giving the cationic complex 5 the X-ray structure of which has revealed metallation at position 4 of the indole hydrazone, which is terdentate forming a [5,6]-fused ring system.

Polyfunctional phosphine ligands II. Iridium(I) complexes of the 7-diphenylphosphino-2,4-dimethyl-1,8-naphthyridine (dpnapy) ligand. X-ray crystal structure of [{Ir(cod)Cl}2(μ-dpnapy)]

Abstract The coordination chemistry of the polyfunctional phosphine ligand, 7-diphenylphosphino-2,4-dimethyl-1,8- naphthyridine (dpnapy) with iridium(I) complexes has been investigated. Dpnapy reacts with cis -[Ir(CO) 2 ( p - toluidine)Cl] in 1:2 and 1:1 molar ratios giving the P-monodentate containing ligand complexes trans - [Ir(CO)(dpnapy) 2 Cl] ( 1 ) and cis -[Ir(CO) 2 (dpnapy)Cl] ( 2 ), respectively. Complex 2 is unstable in solution; IR and 31 P NMR spectroscopic data show at r.t. it transforms into 1 in a short time. The reaction of dpnapy with [{Ir(cod)Cl} 2 ] (cod=cycloocta-1,5-diene) also depends on the metal to ligand ratio used. The mononuclear complex [Ir(cod)(dpnapy)Cl] ( 3 ), containing P-coordinated dpnapy, is obtained from the 1:2 dimer:ligand reaction. The 1 H and 13 C NMR spectra of 3 are temperature dependent. They show that the fluxional behaviour involves the cod ligand and is explained by the formation of a labile five-coordinate intermediate displaying a fast exchange of the non-equivalent cod protons and carbons. Treatment of 3 with AgClO 4 leads to a species, formulated on the basis of IR and analytical data, as [{Ir(cod)(dpnapy)}ClO 4 ] ( 4 ) in which dpnapy is very likely PN(8) chelated. The binuclear complex [{Ir(cod)Cl} 2 (μ-dpnapy)] ( 5 ), containing a bridging bidentate dpnapy, is obtained from the 1:1 [{Ir(cod)Cl}2]:dpnapy reaction. The bridging function of dpnapy is realized through the phosphorus and the terminal nitrogen binding sites in agreement with the NMR data and as confirmed by an X-ray analysis. Complex 5 crystallizes into the monoclinic space group P 2 1 / n with cell parameters a =17.813(4), b =12.339(3), c =18.221(5) A, β=106.73(2)° and with Z =4. The structure model, with all the non-H atoms anisotropic, was refined up to R =0.040 and R w =0.050 with the goodness-of-fit=0.91. The asymmetric unit contains one discrete molecule constitued by two independent square-planar iridium moieties, considering each ethylenic system of cycloocta-1,5-diene like a unique coordination site. No interaction exists between the two iridium metal centres.

Polyfunctional phosphine ligands. Synthesis of 7-diphenylphosphino-2,4-dimethyl-1,8-naphthyridine and its co-ordination properties

The new trinucleating ligand 7-diphenylphosphino-2,4-dimethyl-1,8-naphthyridine (dpnapy) has been prepared and its co-ordination chemistry with rhodium(I) complexes investigated. Reactions with [{Rh(cod)Cl}2](cod = cycloocta-1,5-diene) lead to different products depending on the ligand to metal ratio. The P-monodentate ligand complex [Rh(cod)(dpnapy)Cl]1 is formed when a 2 : 1 ligand : dimer ratio is used. The cod region of the 1H and 13C NMR spectra of 1 is temperature dependent. The fluxional behaviour can be explained by the formation of a five-co-ordinate intermediate displaying rapid intramolecular exchange of the cod olefinic and CH2 protons. A lower activation energy process, not frozen at 215 K, is also observed. At room temperature (r.t.) the two-dimensional 1H and 31P chemical exchange spectra indicate a further slower dynamic equilibrium 1⇌2 with loss of dpnapy. The binuclear complex [{Rh(cod)Cl}2(µ-dpnapy)]2, in which dpnapy acts as bridging bidentate ligand using the phosphorus and the terminal nitrogen atoms, is the reaction product when a 1 : 1 ligand : dimer ratio is used. The 1H and 13C NMR data for complex 2 are consistent with a dimeric structure of low symmetry. Complex 2 is also involved in several dynamic processes. At r.t. the two-dimensional 1H chemical exchange spectrum shows a slow general scrambling of the cod olefinic protons and the presence of the equilibrium 2⇌1 with participation of [{Rh(cod)Cl}2]. The ligand reacts with [{Rh(CO)2Cl}2] giving as the only isolable product the metallocycle [{Rh(CO)(µ-dpnapy)Cl}2]·2CH2Cl23. The reaction proceeds through several steps involving the formation of cis-dicarbonyl intermediates as indicated by IR and NMR spectra. The structure of 3 has been determined by X-ray crystallography. It consists of two Rh(CO)Cl units, joined together by two dpnapy molecules in a head-to-tail arrangement.

Dynamic behaviour and X-ray analysis of chiral η3-allylpalladium complexes. II

Abstract The DANTE technique and NOESY two-dimensional method have been employed to observe the isomerization of the chiral cationic complex [Pd(η 3 -CH 2 CMeCH 2 (P-P′)] + ( 1a ), where P-P′ = the chiral chelating ligand ( S )( N -diphenylphosphino)(2-diphenylphosphinoxymethyl)pyrrolidine. The rate constant was found to be ⪡ 0.5 s −1 in CHCl 3 at 295 K and 1.50 s −1 in the presence of added free ligand. In the latter case the epimerization proceeds by a π-σ-π mechanism via the intermediacy of a primary η 1 -allylpalladium complex. Although the intermediate was not detected, the NMR findings reveal that it has the allylic terminus η 1 -bonded to palladium. The structure of 1a in its PF 6 − salt has been determined. The compound crystallizes in the orthorhombic space group P 2 1 2 1 2 1 with a 10.029(4) b 19.203(8) c 36.115(6) A, Z = 8, R = 0.0572 and R w = 0.0712 for 3716 observed reflections with I > 3σ( I ).

Nuclear magnetic resonance and crystallographic studies of chiral η3-allyl palladium(II) complexes and asymmetric allylic alkylation of propen-2-yl acetates

The chiral complexes [Pd(η3-allyl)(P–P′)]X [P–P′= the chiral chelating ligand (S)(N-diphenylphosphino)(2-diphenylphosphinoxymethyl)pyrrolidine; allyl = MeCHCHCHMe, 2; or PhCHCHCHPh 3; X = BF4– or PF–6] have been prepared and analysed by NMR spectroscopy. Their diastereoisomeric composition have been determined on the basis of 1H, 13C, 31P and two-dimensional 1H–X (X =13C or 31P) correlation NMR spectra. Since retention of the preferred syn disposition of the allylic substituents occurs in both cases the reaction product is a mixture of two isomers which differ in allylic chirality. The relative absolute configurations have been assigned by two-dimensional nuclear Overhauser effect measurements and confirmed by the X-ray crystallographic determination of the structure of the major diastereoisomer of 2: the allyl fragments have (1S,3R) absolute configuration. The reaction of racemic 1,3-dimethylprop-2-enyl acetate in the presence of 2 and of 1,3-diphenylprop-2-enyl acetate in the presence of 3 with sodium dimethyl malonate gives the allylic alkylation products in 20 and 30% enantiomeric excess respectively.

Crystallographic and nuclear magnetic resonance studies of carbonyl(η3-methylallyl)(trichlorostannyl) complexes of platinum(II) and palladium(II)

The complexes [M(η3-C4H7)(SnCl3)(CO)][C4H7= 2-methylallyl, M = Pt(1) or Pd(2)] have been prepared and characterized. Their solution behaviour has been studied by n.m.r. spectroscopy, the compounds being dynamic through dissociation of the CO ligand. The X-ray structures of (1) and (2) are reported. Complex (2) is the first mononuclear palladium carbonyl to be characterized by X-ray diffraction. The different stabilities of the two isostructural complexes are correlated with the subtle differences in bonding observed in the crystal structures.

Synthesis of (+)-(3S,7S,10S)- and (+)-(3S,7S,10R)-3,7,10-trimethylboratrane. Amplification of enantiomeric purity in the reacti

Abstract The synthesis is described of the two enantiomerically pure isomers (+)-(3 S ,7 S ,10 S )- and (+)-(3 S ,7 S ,10 R )-3,7,10-trimethylboratr The structures were determined by 1 H- and 13 C-NMR spectroscopy. A method for increasing the enantiomeric purity by trimerization reactions of partially-resolved ( S ) propylene oxide is proposed. The reaction was studied from the kinetic viewpoint and interpreted according to a binomial probability scheme. The experimental findings point to a rapid growth in enantiomeric purity for the ( SSS ) trimer compared with the starting material, whilst no increase was found for the ( SSR ) trimer.

Palladium(II) and platinum(II)η3-methylallyl trichlorotin complexes. Part 3. Crystal structure analysis of [Pt(η3-C4H7)(cod)]2[Pt(η3-C4H7)(SnCl3)3](cod = cyclo-octa-1,5-diene)

The dimer [{Pt(η3-C4H7)Cl}2] reacts with cyclo-octa-1,5-diene (cod) and SnCl2 to give [Pt(η3-C4H7)(cod)]2[Pt(η3-C4H7)(SnCl3)3](1). The compound crystallizes as discrete anionic and cationic platinum(II) complexes in space group P with a= 13.256(4), b= 19.960(4), c= 8.615(3)A, α= 101.75(2), β= 104.69(2), and γ= 86.62(2)°. The anionic complex displays a distorted square-pyramidal co-ordination while the two isostructural cations have irregular square-planar co-ordination. Analysis of bond distances using SnCl3 as a probe suggests that the trans influence of the methylallyl ligand is comparable to that of olefin ligands. While no n.m.r. data are available for (1) due to its very poor solubility, n.m.r. results for the palladium(II) analogue (2) obtained by the same synthetic route are compatible with the structure determined for (1).

The Dynamic Behaviour of η3-Allyl Palladium and Platinum Complexes Containing the SnCl3 Ligand

Abstract The solution behaviour of [η3-allylM(PR3)SnCl3] (M = Pd, Pt) has been studied. Dissociation of the Sn ligand (either SnCl2 or SnCl3) explains the dynamic behaviour observed by NMR. The M-Sn bond is stronger if an alkylphosphine is bound to the metal. According to the observed 1J(Pt, C) values of the Pt-C bond trans to SnCl3, tin ligand and olefin have comparable trans influence.

The insertion of cycloheptatriene and cyclohepta-1,3-diene into the RuH bond of RuHCl(PPh3)3 to give Ru(η5-C7H9)Cl(PPh3)2 and Ru(η3-C7H11)Cl(PPh3)2

Abstract RuHCl(PPh 3 ) 3 reacts quantitatively with cycloheptatriene in CH 2 Cl 2 at 35°C in 15 min to give Ru(η 5 -C 7 H 9 )Cl(PPh 3 ) 2 and PPh 3 . The major isomer adopts a conformation with inequivalent phosphorus ligands and no plane of symmetry through the C 7 H 9 ligand, but rapid intramolecular scrambling with δ G ‡ = 10.6 kcal mol −1 results in an averaged 1 H, 13 C, and 31 P NMR spectrum at room temperature. RuHCl(PPh 3 ) 3 reacts with cyclohepta-1,3-diene to give initially Ru(η 3 -C 7 H 11 )Cl(PPh 3 ) 2 , but in a subsequent reaction this is dehydrogenated to give Ru(η 5 -C 7 H 9 )Cl(PPh 3 ) 2 .