Paul S. Pregosin

STRUCTURE AND DYNAMICS OF CHIRAL ALLYL COMPLEXES OF PD(II) : NMR SPECTROSCOPY AND ENANTIOSELECTIVE ALLYLIC ALKYLATION

Abstract The idea of NOE ‘reporter ligands’, be they simple nitrogen chelates or relatively complicated bidentate phosphine compounds, is explored. These NMR experiments lead to a better understanding of subtle (allyl hybridization, phenyl-phenyl stacking) and gross (three-dimensional aspects, shape of the chiral pocket) structural features in the chemistry of chiral palladium-allyl complexes. Combined with X-ray crystallography and MM2∗ calculations, one can learn how the BINAP, CHIRAPHOS and JOSIPHOS families of chiral ligands use steric effects to transfer chiral information. A relatively rigid chiral pocket seems a necessary, but not sufficient, condition, since an intrusive chiral pocket leads to syn-anti isomers. Two-dimensional exchange NMR has shown unexpected selectivity with respect to allyl isomerization. The η3-η1 isomerization can be under either electronic or steric control. The terminal allyl 13C chemical shifts in 1,3-diphenylallyl palladium(II) complexes of various chelate ligands are discussed.

Fast and Highly Regioselective Allylation of Indole and Pyrrole Compounds by Allyl Alcohols Using Ru-Sulfonate Catalysts

New Ru-sulfonate catalysts have been synthesized and shown to very rapidly allylate indole and pyrrole compounds using allyl alcohols as substrates. The observed regioselectivity is exceptionally high (up to 100% of the branched isomer). Density functional theory calculations explain these results.

Complexation of an amide to iridium via an iminol tautomer and evidence Ir–H ⋯ H–O hydrogen bond

The OH group of the iminol complex [IrH2L′(PPh3)2]SbF6·2H2O where L′ is the iminol tautomer of quinolin-8-acetamide, takes part in an O–H ⋯ H–Ir hydrogen bond.

31P and 195Pt NMR studies of the cluster complexes [Pt3(μ2-CO)3 (tertiary phosphine)3]

Abstract 31P and 195Pt NMR data for the triangular clusters [Pt3(μ2-CO)3(tertiary phosphine)3] tertiary phosphine = PCy3, PPri3, PPri2Ph, P(CH2Ph)Ph2, are reported. The nuclearity of the complexes in solution is readily identified via 31PNMR using the multiplicity data in the 195Pt satellites. The values 1J(195Pt, 195Pt) have been measured and fall in the range 1571–1619 Hz. It is suggested that the values 2J(195Pt, 31P) and 3J(31P, 31P) can be useful indicators for the presence of platinum—platinum bonds.

Facile cycloplatination of nitrogen compounds. Crystal structure of the cycloplatinated Schiff's base tetralone derivative PtCl{(cyclohexyl)NC(CH2)3C6H3 (CO)

Abstract Facile preparative methods for the cycloplatination of benzo[ c ]quinoline ( 1 ), two Schiffs base tetralone compounds, R 1 NC(CH 2 ) 3 C 6 H 4 (R 1 = cyclohexyl ( 2 ), CH 2 ( p -C 6 H 4 OCH 3 ) ( 3 )), and 8-methylquinoline ( 4 ), are given. An extension of these methods leads readily to new cycloplatination chemistry involving use of 1 or 3 or quinoline-8-carboxaldehyde and the cycloplatinated phosphite complex [Pt(μ-Cl){(R 2 O) 2 POC 6 H 4 ]] 2 , R 2 = Et, Ph, to give the complexes Pt(NO 3 )( CN ){P(OPh)(OR) 2 }, where ( CN ) denotes the cycloplatinated nitrogen-ligand. The molecular structure of PtCl{(cyclohexyl)NC(CH 2 ) 3 C 6 H 3 ](CO) has been determined by X-ray diffraction.

Palladium(II) complexes of chiral tridentate nitrogen pybox ligands

A series of mono- and di-cationic palladium(II) complexes containing different chiral tridentate nitrogen ligands, pybox, have been prepared [pybox = 2,6-bis[4′-(S)-iPr (or Ph, or Bz or p-EtOC6H4)oxazoline-2′-yl]pyridine (1–4), respectively]. The molecular structures for two of these, [Pd(CH3CN)(2)](BF4)2 (6) and [Pd(PPh3)(3)](BF4)2 (21g), have been determined by X-ray diffraction and show no major steric hindrance in the fourth coordination position. In connection with the aldol reaction of CNCH2CO2Me with PhCHO, several new isonitrile PdII complexes have also been prepared. It is shown that, under catalytic conditions, the chiral tridentate pybox ligand is completely displaced, thus explaining its failure as a chiral auxiliary. Preparative details for a series of chiral Pd(L)(3)n+(BF4)n (21) complexes [L = 4-methylpyridine, 2,6-dimethylpyridine, 4-methyl aniline, H2NCH2CH(OMe)2, H2NCH2CH2OH, H2N(CH2)5CH3, N3−, HCO2−] Cl−] are given, as are preparative details for some model PdII acetonitrile complexes with chiral phosphorus and nitrogen chelating ligands. For 6, i.e. PdC25H22N4O2B2F8, the crystals are monoclinic with space group P21 (No. 4), a = 13.582(6) A, b = 13.826(6) A, c = 14.667(6) A, β = 97.28(3)°, V = 2732(2) A3, Z = 4. For 21g, i.e. C43H38B2F8N3O2P2Pd, the crystals are orthorhombic with space group, P212121, a = 10.616(4) A, b = 16.774(2) A, c = 23.086(4) A, V = 4111(3) A3, Z = 4.

Platinum-promoted cyclization reactions of amino olefins : II. Regio- and stereoselectivity in the cyclization reactions of C-methyl substituted pent-4-enylamines

Abstract The compounds 1-, 2- and 3-methylpent-4 enylamine cyclize, in a reaction medium containing [PtCl4]2-, to the corresponding cis- and trans-dimethylpyrrolidines showing marked regio and stereoselectivity effects. The following cyclization reactions are also reported: a) that of hex-4-enylamine which gives a mixture of 2-ethylpyrrolidine and 2-methylpiperidine, b) that of 2,2-dimethylpent-4-enylamine which produces 2,4,4-trimethylpyrrolidine and c) that of 2,2-dimethylhex-4-enylamine which results in the formation of 2-ethyl-4,4-dimethylpyrrolidine and 2-methyl-5,5-dimethylpiperidine. The X-ray crystal structures of trans-[PtCl2(amine)(Et3P)] (amine = cis-2, 4-dimethylpyrrolidine and cis-2,3-dimethylpyrrolidine) are reported.

Fast Ruthenium‐Catalysed Allylation of Thiols by Using Allyl Alcohols as Substrates

Green and fast: Allylation of aromatic and aliphatic thiols, by using allyl alcohols as substrates, requires only minutes at ambient temperature with a Ru catalyst (see scheme). Quantitative conversion is normal and the catalyst possesses high functional-group tolerance.The allylation of aromatic and aliphatic thiols, by using allyl alcohols as substrates, requires only minutes at ambient temperature with either a Ru(IV) catalyst, [Ru(Cp*)(eta(3)-C(3)H(5))(CH(3)CN)(2)](PF(6))(2) (2; Cp*=pentamethylcyclopentadienyl) or a combination of [Ru(Cp*)(CH(3)CN)(3)](PF(6)) and camphor sulfonic acid. Quantitative conversion is normal and the catalyst possesses high functional-group tolerance. The use of [Ru(Cp*)(CH(3)CN)(3)](PF(6)) alone affords poor results. A comparison is made to the results from catalytic runs based on the use of carbonates rather than alcohols, by using 2 as the catalyst, and it is shown that the products from the alcohols are formed faster, so there is no advantage in using a carbonate substrate. The observed branched-to-linear (b/l) ratios when using substituted alcohols decrease with time suggesting that the catalysts isomerise the products. A new methodology from which one can select the desired isomeric product is proposed. DFT calculations and NMR spectroscopic measurements, by using an arene sulfonic acid as co-catalyst, suggest that eta(6)-complexes are not relevant for the catalytic system. Moreover, the DFT results indicate that 1) any eta(6)-complexes from the acids RC(6)H(4)SO(3)H result from deprotonation of the acid, 2) complexation of the thiol, via the deprotonated sulfur atom, is preferred over complexation of the O atom of the sulfonate, RC(6)H(4)SO(3) (-) and 3) a sulfonate O-atom complex will be difficult to detect.

A convenient preparation of dinuclear Pt(II) phosphine complexes

Abstract A simple one-step method for the preparation of dinuclear chloro-bridged platinum(II) phosphine complexes, [Pt(μ-Cl)Cl(PR3)]2 is reported. The syntheses are carried out in p-chlorotoluene and are reported for the following tertiary phosphines: PMe2Ph, P(p-Tol)3, PPh3, PBun3 and PEt3.

31P and 195Pt NMR studies on the clusters [Pt4(μ2-CO)5L4]. L=PEt3, PMe2Ph, PMePh2, PEt2But: the molecular structure of a monoclinic modification of [Pt4(μ2-CO)5(PMe2Ph)4]

Abstract Several clusters complexes of composition [Pt4(μ2-CO)5L4] have been synthesized and characterized, using 31P and 195Pt NMR. L = PEt3, PMe2Ph, PMePh2, PEt2But. The molecular structure of a new monoclinic modification of the PMe2Ph derivative has been determined: space group P21/n with a = 19.698(4), b = 10.9440(20), and c = 21.360(6) A, β = 112.432(18)°, Z = 4. Using 4751 reflections measured at 290 ± 1 K on a four-circle diffractometer the structure has been refined to R = 0.0846. The molecule has no imposed symmetry, but the central Pt4(CO)5P4 core has the approximate C2v architecture established for the previously known orthorhombic modification. The Pt4 unit is thus a highly distorted, edge-opened (3.3347 A) tetrahedron, with five edge-bridging carbonyl and four terminal phosphine ligands. In contrast to the crystallographic results 31P and 195Pt NMR spectra reveal equivalent 31P and 195Pt spins, which can be interpreted in terms of a tetrahedral arrangement of platinum atoms. It is suggested that this equivalence arises from time-averaging of all possible isomeric edge-opened tetrahedra.