A hybrid bipy–NHC ligand for the construction of group 11 mixed-metal bimetallic complexes

An asymmetric bipy/NHC ligand L has been used to construct Au/Au, Au/Ag and Au/Cu bimetallic complexes through prior coordination of the NHC to Au(i) and subsequent introduction of the second group 11 metal ion at the bipy donor of the hybrid ligand. The complex [Au(κ^C-L)₂]BF_4,1, has been used as the precursor for the formation of [AuAg(κ-C^Au,κ²-N,N′^Ag-1)₂](BF₄)₂, 2a, [AuCu(κ-C^Au,κ²-N,N′^Cu-1)₂](BF₄)₂, 2b and [AuAu′(κ-C^Au/Au′,κ¹-N^Au/Au′-1)₂](BF₄)₂, 3.

A ditopic bipy–NHC ligand has been used to construct hetero-bimetallic complexes of the monovalent group 11 metals.

Organodiphosphines in Pt{η2-P(X)nP}Cl2 (n = 9–15, 17, 18) derivatives – Structural aspects

This review covers over 20 monomeric platinum complexes of Pt{η2-P(X)nP}Cl2 (n = 9–15, 17, 19) type. The chelating P,P-donor ligands create wide varieties of the metallocyclic rings: 12-membered (PC9P, PC3NCNC3P), 13-membered (PC3NC2NC3P), 14-membered (PC11P, PO(SiO)5P, PC2OC2OC2OC2P), 15-membered (PC12P), 16-membered (PCOC9OCP), 17-membered (P(C2O)4C2P), 18-membered (PC2OC9OC2P, PC4NC2NC2NC4P), 20-membered (P(C2O)5C2P), and 21-membered (POC2NC10NC2OP). For these complexes the most common is a predominantly cis-arranged with 17 examples and only four examples with trans-configuration. The total mean values of Pt–L bond distances in the complexes with cis- versus trans-configuration are: 2.252 Å (P trans to Cl), 2.355 Å (Cl trans to P) vs 2.288 Å (P trans to P), and 2.304 Å (Cl trans to Cl). There are examples which exist in cis- and trans-isomeric forms and distortion isomers. A brief survey on the structural data of almost 180 examples of Pt{η2-P(X)nP}Cl2 (n = 1–8) type complexes is added and discussed.

Synthesis of Camphor-Derived Bis(pyrazolylpyridine) Rhodium(III) Complexes: Structure-Reactivity Relationships and Biological Activity

Two novel rhodium(III) complexes, namely, [Rh^III(X)Cl₃] (X = 2 2,6-bis((4 S,7 R)-7,8,8-trimethyl-4,5,6,7-tetrahydro-1 H-4,7-methanoindazol-3-yl)pyridine or 2,6-bis((4 S,7 R)-1,7,8,8-tetramethyl-4,5,6,7-tetrahydro-1 H-4,7-methanoindazol-3-yl)pyridine), were synthesized from camphor derivatives of a bis(pyrazolylpyridine), tridentate nitrogen-donor chelate system, giving [Rh^III(H₂L*)Cl₃] (1a) and [Rh^III(Me₂L*)Cl₃] (1b). A rhodium(III) terpyridine (terpy) ligand complex, [Rh^III(terpy)Cl₃] (1c), was also synthesized. By single-crystal X-ray analysis, 1b crystallizes in an orthorhombic P2₁2₁2₁ system, with two molecules in the asymmetric unit. Tridentate coordination by the N,N,N-donor localizes the central nitrogen atom close to the rhodium(III) center. Compounds 1a and 1b were reactive toward l-methionine (l-Met), guanosine-5'-monophosphate (5'-GMP), and glutathione (GSH), with an order of reactivity of 5'-GMP > GSH > l-Met. The order of reactivity of the Rh^III complexes was: 1b> 1a > 1c. The Rh^III complexes showed affinity for calf thymus DNA and bovine serum albumin by UV-vis and emission spectral studies. Furthermore, 1b showed significant in vitro cytotoxicity against human epithelial colorectal carcinoma cells. Since the Rh^III complexes have similar coordination modes, stability differences were evaluated by density functional theory (DFT) calculations (B3LYP(CPCM)/LANL2DZp). With (H₂L*) and (terpy) as model ligands, DFT calculations suggest that both tridentate ligand systems have similar stability. In addition, molecular docking suggests that all test compounds have affinity for the minor groove of DNA, while 1b and 1c have potential for DNA intercalation.

A camphor based 1,3-diamine Ru(ii) terpyridine complex: synthesis, characterization, kinetic investigation and DNA binding

A chiral ancillary ligand that has more steric bulk results in an increased reactivity of a ruthenium complex with biomolecules.

Mono- and dimeric complexes of an asymmetric heterotopic P,CNHC,pyr ligand

An asymmetric heterotopic ligand (S-N(Me)CP) containing a central bicyclic, expanded-ring NHC with one pyridyl and one phosphine exo-substituent has been synthesised and its coordination chemistry with selected late transition metals investigated. The amidinium precursor [S-N(Me)CHP]PF6 shows variable coordination modes with Ag(i), Cu(i) and Au(i) depending on the L : M ratio. The reaction of two mols of [S-N(Me)CHP]PF6 with [Cu(MeCN)4]BF4, AgBF4 or Au(THT)Cl gives the bis-ligand complexes [Cu(κ-P-N(Me)CHP)2(CH3CN)2]BF4·(PF6)2, 1, and [M(κ-P-N(Me)CHP)2]X·(PF6)2 (3: M = Ag, X = BF4; 6: M = Au, X = Cl) respectively. The 1 : 1 reaction of [S-N(Me)CHP]PF6 with AgOTf gave the head-to-tail dimer H,T-[Ag2(μ-N,P-N(Me)CHP)2(μ-OTf)2](PF6)2, 2, whereas the analogous reaction with Au(THT)Cl gave monomeric [Au(κ-P-N(Me)CHP)Cl]PF6, 5. Complex 2 was converted to H,T-[Ag2(μ-C,P-N(Me)CP)2](PF6)2, 4, upon addition of base, while 6 gave [Au(κ-C-N(Me)CP)2]Cl, 8, when treated likewise. Reaction of [S-N(Me)CHP]PF6 with Ni(1,5-COD)2 gave the oxidative addition/insertion product [Ni(κ(3)-N,C,P-N(Me)CP)(η(3)-C8H13)]PF6, 9, which converted to [Ni(κ(3)-N,C,P-N(Me)CP)Cl]PF6, 10, upon exposure of a CHCl3 solution to air. Complex 10 showed conformational isomerism that was also present in [Rh(κ(3)-N,C,P-N(Me)CP)(CO)]PF6, 14, prepared from the precursor complex [Rh(κ-P-N(Me)CHP)(acac)(CO)]PF6, 13, upon heating in C6H5Cl. [Pt(κ(3)-N,C,P-N(Me)CP)(Cl)]PF6, 12, derived from trans-[Pt(κ-P-N(Me)CHP)2(Cl)2](PF6)2, 11, was isolated as a single conformer.

N2S2 and N4S4 precursors to PS2 macrocycles and cyclic amidinium salts

The cyclo-condensation of 1R,2R-diaminocyclohexane with 2,2'-(ethane-1,2-diyldisulfanediyl)dibenzaldehyde gave the 1 : 1 addition compound chxn-(im)N2S2 in high yield. When the same condensation reaction was performed with 1R,3S-diamino-1,7,7-trimethylcyclopentane as the diamine, the 2 : 2 addition compound tmcp-(im)N4S4 was obtained selectively. Reduction of the diimines gave the saturated analogues chxn-N2S2 (1) and tmcp-N4S4 (3) the former of which could be phosphorylated with PhP(NMe2)2 to give the novel 13-membered macrocycle chxn-PS2, 2. Introduction of the phenylphosphine function proved stereoselective with a preference for the N(R)/N(S) configuration at the nitrogen atoms. The coordination chemistry of the novel phosphine has been explored with Cu(i) and Mo(0) through formation of the complexes Cu(2)I, 4, and Mo(CO)3(2), 5. Extension of the phosphorylation chemistry to tmcp-N4S4 (3) proved unsuccessful but ring closure reactions of both 1 and 3 with triethylorthoformate gave cyclic amidinium salts which are potential precursors to macrocyclic N-heterocyclic carbenes.

Cationic mono and dicarbonyl pincer complexes of rhodium and iridium to assess the donor properties of PCcarbeneP ligands

The donor properties of five different PC_carbeneP ligands are assessed by evaluation of the CO stretching frequencies in iridium(i) and rhodium(i) carbonyl cations.

It's all about Me: methyl-induced control of coordination stereochemistry by a flexible tridentate N,C,N' ligand

A chiral, tridentate, pyridyl-functionalised NHC pro-ligand, S-L(Me)-H[PF₆], has been prepared diastereoselectively via a five step synthesis starting from 1R,3S-diamino-1,2,2-trimethylcyclopentane. The S prefix refers to the stereochemistry of a methyl substituted stereogenic carbon in one of the pyridyl arms which is generated by a stereoselective BH4(-) reduction of an imine precursor. The ligand has been coordinated to Rh(I) and Ir(I) to give trigonal bipyramidal complexes of the type [M(κ(3)-N,C,N'-S-L(Me))(1,5-COD)]PF6 (M = Rh, Ir) as single diastereomers. A combination of spectroscopic and X-ray techniques confirm the stereoselective formation of the thermodynamically preferred endo,endo isomer. Similar reactions with R,S-L(Me)-H[PF₆] gave a mixture of endo,endo-[M(κ(3)-N,C,N'-S-L(Me))(1,5-COD)](+) and exo,exo-[M(κ(3)-N,C,N'-R-L(Me))(1,5-COD)](+). The absolute configuration at the metal is, therefore, solely dictated by the stereochemistry of the single methylpyridyl carbon. The observation of stereoselection extends to the square planar Ni(II) complex [Ni(δ-κ(3)-N,C,N'-S-L(Me))Cl](+) which is isolated as one (δ) of the two possible conformational isomers. DFT studies have been employed to explain the observed stereoselectivity with the configurations observed in the solid state being confirmed as those of lowest energy.

N-alkyl functionalised expanded ring N-heterocyclic carbene complexes of rhodium(I) and iridium(I): structural investigations and preliminary catalytic evaluation

A series of new N-alkyl functionalised 6- and 7-membered expanded ring N-heterocyclic carbene (NHC) pro-ligands 3-6 and their corresponding complexes of rhodium(I) and iridium(I), [M(NHC)(COD)Cl] 7-14 and [M(NHC)(CO)2Cl] 15-22 are described. The complexes have been characterised by (1)H and (13)C{(1)H} NMR, mass spectrometry, IR and X-ray diffraction. It is noted from X-ray diffraction studies that the N-alkyl substituents are found to orientate themselves away from the metal centre due to unfavourable steric interactions resulting in low percent buried volume (%V(bur)) values in the solid state. The heterocycle ring size is also found to dictate the spatial orientation of the N-alkyl substituents in the neopentyl functionalised derivatives 10 and 14. The 7-membered derivative 14 allows for a conformational 'twist' of the heterocycle ring with the N-alkyl substituents adopting a mutually trans configuration with respect to each other, while the more rigid 6-membered system 10 does not allow for this conformational 'twist' and consequently the N-alkyl substituents adopt a mutually cis configuration. The σ-donor function of this new class of expanded ring NHC ligand has also been probed by measured IR stretching frequencies of the [M(NHC)(CO)2Cl] complexes 15-22. A preliminary catalytic survey of the hydrogenation of functionalised alkenes with molecular hydrogen under mild conditions has also been undertaken with complex , affording an insight into the application of large ring NHC ancillary ligands bearing N-alkyl substituents in hydrogenation transformations.