A new family of flexible scorpionate ligands based on 2-mercaptopyridine is reported. The tris- and bis-substituted ligands, K[HB(mp)(3)] (1) and Na[H(2)B(mp)(2)] (2) (mp = 2-mercaptopyridine) have been prepared and fully characterised. The structural characterisation of 1 reveals an unprecedented mu(3)-kappa(3)-SS'H-eta(1)eta(1)eta(2)-kappa(2)-S''C-eta(1)eta(1)-kappa(1)-S'-eta(1) coordination mode. The coordination of both 1 and 2 to copper(I) complexes containing triphenylphosphine and tricyclohexylphosphine co-ligands is investigated suggesting kappa(3)-SSS coordination modes for [Cu{HB(mp)(3)}(PR(3))] {where R = Ph (3); R = Cy, (4)} and kappa(3)-SSH coordination modes for [Cu{H(2)B(mp)(2)}(PR(3))] {where R = Ph (5); R = Cy (6)} the latter confirmed by structural characterisation of 5. A structural comparison with the sulfur based scorpionates, HB(mt)(3) and H(2)B(mt)(2) (mt = methyl-2-mercaptoimidazole) is made in terms of the degree of tautomerisation of the heterocyclic rings.

A Cp*Co -catalyzed C-H functionalization of benzamide substrates with α,β-unsaturated ketones has been optimized, providing a facile route towards aliphatic ketone products. When employing α,β-unsaturated aldehydes as coupling partners, under the optimized protocol, a cascade reaction forming azepinones has also been developed. Finally, DFT studies have demonstrated how stabilization of a metallo-enol intermediate when employing α,β-unsaturated ketones is the driving force leading to the observed aliphatic ketone product rather than olefinic products reported using α,β-unsaturated esters as coupling partners.

Three methods for the large scale (50-100 g) separation of the secondary phobanes 9-phosphabicyclo[3.3.1]nonane (s-PhobPH) and 9-phosphabicyclo[4.2.1]nonane (a-PhobPH) are described in detail. Selective protonation of s-PhobPH with aqueous HCl in the presence of a-PhobPH is an efficient way to obtain large quantities of a-PhobPH. Selective oxidation of a-PhobPH in an acidified mixture of a-PhobPH and s-PhobPH is an efficient way to obtain large quantities of s-PhobPH. The crystalline, air-stable phosphonium salts [s-PhobP(CH(2)OH)(2)]Cl and [a-PhobP(CH(2)OH)(2)]Cl can be separated by a selective deformylation with aqueous NaOH. a-PhobPH is shown to be a(5)-PhobPH in which the H lies over the five-membered ring. The isomeric a(7)-PhobPH has been detected but isomerizes to a(5)-PhobPH rapidly in the presence of water. s-PhobPH is more basic than a-PhobPH by about 2 pK(a) units in MeOH. Treatment of s-PhobPH with BH(3).THF gives s-PhobPH(BH(3)) and similarly a-PhobPH gives a(5)-PhobPH(BH(3)). Isomerically pure s-PhobPCl and a(5)-PhobPCl are prepared by reaction of the corresponding PhobPH with C(2)Cl(6). The n-butyl phobane s-PhobPBu is prepared by nucleophilic (using s-PhobPH or s-PhobPLi) and electrophilic (using s-PhobPCl) routes. Isomerically pure a(5)-PhobPBu is prepared by treatment of a-PhobPLi with (n)BuBr and a(7)-PhobPBu is prepared by quaternization of a-PhobPH with (n)BuBr followed by deprotonation. From the rates of conversion of a(7)-PhobPBu to a(5)-PhobPBu, the DeltaG(double dagger) (403 K) for P-inversion is calculated to be 38.1 kcal mol(-1) (160 kJ mol(-1)). The donor properties of the individual isomers of PhobPBu were assessed from the following spectroscopic measurements: (i) (1)J(PSe) for PhobP(Se)Bu; (ii) nu(CO) for trans-[RhCl(CO)(PhobPBu)(2)], (iii) (1)J(PtP) for the PEt(3) in trans-[PtCl(2)(PEt(3))(PhobPBu)]. In each case, the data are consistent with the order of sigma-donation being a(7)-PhobPBu > s-PhobPBu > a(5)-PhobPBu. This same order was found when the affinity of the PhobPBu isomers for platinum(II) was investigated by determining the relative stabilities of [Pt(CH(3))(s-PhobPBu)(dppe)][BPh(4)], [Pt(CH(3))(a(5)-PhobPBu)(dppe)][BPh(4)], and [Pt(CH(3))(a(7)-PhobPBu)(dppe)][BPh(4)] from competition experiments. Calculations of the relative stabilities of the isomers of PhobPH, [PhobPH(2)](+), and PhobPH(BH(3)) support the conclusions drawn from the experimental results. Moreover, calculations on the frontier orbital energies of PhobPMe isomers and their binding energies to H(+), BH(3), PdCl(3)(-), and PtCl(3)(-) corroborate the experimental observation of the order of sigma-donation being a(7)-PhobPR > s-PhobPR > a(5)-PhobPR. The calculated He(8) steric parameter shows that the bulk of the isomers increases in the order a(7)-PhobPR < s-PhobPR < a(5)-PhobPR. The crystal structures of [a-PhobP(CH(2)OH)(2)][s-PhobP(CH(2)OH)(2)]Cl(2), cis-[PtCl(2)(a(5)-PhobPCH(2)OH)(2)], trans-[PtCl(2)(s-PhobPBu)(2)], and trans-[PtCl(2)(a(7)-PhobPBu)(2)] are reported.

The 9-amino(9-deoxy)epi cinchona alkaloids have expanded the synthetic potential of asymmetric aminocatalysis, enabling the highly stereoselective functionalization of a variety of sterically hindered carbonyl compounds. However, there is a lack of basic understanding of the mechanisms of cinchona-based primary aminocatalysis. Herein, we describe how a combination of experimental and theoretical mechanistic studies has revealed the origin of the stereoselectivity of the Friedel-Crafts alkylation of indoles with α,β-unsaturated ketones catalyzed by 9-amino(9-deoxy)epi quinine. An essential role for the achiral acid cocatalyst is uncovered: upon condensation of the cinchona catalyst with the enone, the resulting covalent imine intermediate and the acid interact to build-up a well-structured ion-pair supramolecular catalytic assembly, which is stabilized by multiple attractive noncovalent interactions. All the components of the assembly cooperatively participate in the stereocontrolling event, with the anion of the achiral acid being the structural element responsible for the π-facial discrimination of the iminium ion intermediate.

An unusual ruthenium(ii) complex frozen at an intermediate point of hydride transfer between boron and ruthenium centres is reported.

A new boron-based flexible scorpionate ligand based upon 7-azaindole, Li[Ph(H)B(azaindolyl)2] (Li[ Ph Bai]), has been prepared. This ligand, together with the previously reported ligand K[HB(azaindolyl)3] (K[Tai]), have been used to prepare a range of monovalent group 9 transition-metal complexes. The complexes [M(COD){κ3 N,N,H-Ph(H)B(azaindolyl)2}] (where M = rhodium, iridium and COD = 1,5-cyclooctadiene) and [Rh(NBD){κ3 N,N,H-HB(R)(azaindolyl)2}] (where NBD = 2,5-norbornadiene and R = Ph, azaindolyl) have been prepared. Structural characterization of [M(COD){κ3 NNH-Ph(H)B(azaindolyl)2}] (where M = rhodium, iridium) and [Rh(NBD){κ3 N,N,H-HB(azaindolyl)3}] reveal strong interactions of the B−H functional group with the metal centers, particularly in the case of [Ir(COD){κ3 N,N,H-Ph(H)B(azaindolyl)2}]. The complex [Rh(NBD){κ3 N,N,H-HB(azaindolyl)3}] undergoes a further reaction, resulting from hydride migration from boron to the norbornadiene group. Subsequent rearrangement results in the formation of the rhodium−nortricyclyl complex [Rh(nortricyclyl){κ4 N,N,B,N-B(azaindolyl)3}], providing the first nitrogen-based metallaboratrane complex to contain the tetradentate (κ4 N,N,B,N) coordination mode.

Rhodium and iridium complexes of flexible scorpionate ligands based on azaindole were synthesised in good yields. The complexes were characterised in solution and in the solid state. Structural characterisation revealed a B-H-metal interaction, which is retained in solution. Given the greater flexibility of the ligand and potential cooperative effect of boron, the complexes were tested for their activity in the transfer hydrogenation of ketones.

The coordination chemistry and ethene hydromethoxycarbonylation catalysis with the diphosphine o-C 6 H 4 (CH 2 P t Bu 2 )(CH 2 PPh 2 ) (L 3 ) is reported and the results compared with the analogous chemistry of the symmetrical diphosphines o-C 6 H 4 (CH 2 P t Bu 2 ) 2 (L 1 ) and o-C 6 H 4 (CH 2 PPh 2 ) 2 (L 2 ). Palladium-catalyzed ethene hydromethoxycarbonylation studies under the commercial catalytic conditions are reported. The results obtained using L 1-3 as supporting ligands show that the catalysts derived from L 3 and L 1 have similar activity and selectivity for methyl propanoate (MeP). In addition, the Pd-L 3 catalyst has much greater longevity than the Pd- 6), and [PtCl(CH 3 )(L 3 )] (9). At equilibrium, complex 9 is a 90:1 mixture of geometric isomers 9a (with CH 3 trans to the t Bu 2 P) and 9b (with Cl trans to the t Bu 2 P). The fluxionality of complex 3, detected by 1 H NMR, is interpreted in terms of the conformation of the seven-membered chelate. The complexes [Pt(CH 3 )(PMe 3 )(L 3 )]Cl (10b) and [PtH(PPh 3 )(L 3 )]Cl (12b) are formed as essentially single isomers with CH 3 /H trans to the Ph 2 P group. The palladium complexes [PdCl 2 (L 3 )] ( 13), [PdCl(CH 3 )(L 3 )] (14a/14b), and [PdH(PCy 3 )-(L 3 )]BF 4 (15b) have been made by similar methods to their platinum analogues. The factors controlling the relative isomer stabilities are explored experimentally and computationally. The complexes [PtCl 2 (L 4 )] ( 16) and [PtCl(CH 3 )(L 4 )] (17a/17b) where L 4 = o-C 6 H 4 (CH 2 P n Bu 2 )(CH 2 PPh 2 ) are reported, and the geometric isomers of 17 are almost isoenergetic. The crystal structures of 3, 14a, 15b, and 16 have been determined by X-ray crystallography. DFT calculations on complexes of the type [Pt(X)(Y)(L 3 )] gave only small calculated differences in energy between the geometrical isomers (0-4 kcal mol -1 ), which are consistent with the experimental observations. It is suggested that repulsive intramolecular H 3 3 3 H interactions (between the Pt-CH 3 and PC(CH 3 ) 3 groups) determine which isomer predominates. The reasons for the favorable catalytic properties of the Pd-L 3 catalyst are probed by 13 CO reactions with the model complexes 9a/9b and 14a/14b, and the structures of the resulting acyl complexes are assigned on the basis of 13 C and 31 P NMR and IR spectroscopy. From these studies, it is suggested that the reason for the Pd-L 3 catalyst resembling the Pd-L 1 catalyst in terms of selectivity is that the crucial acyl intermediates are similar.