Ringing the Changes: Effects of Heterocyclic Ring Size on Stereoselectivity in [(η-CMe)RhCl], [(η-CMe)IrCl] and [Ru(η-cymene)Cl] Complexes of Chiral 3-Amino-1-Azacycles.

Ring size-dependent diastereoselective coordination of unsymmetrical diamines containing one azacyclic nitrogen and one exocyclic nitrogen to [(η-CMe)MCl] cores where M = Rh, Ir and [Ru(η-cymene)Cl] is reported herein. Total stereoselectivity was observed with the six- and seven-membered azacycles, whereas the five-derivative proved poorly selective. All complexes were active for transfer hydrogenation but showed no enantioselectivity with prochiral ketones.

A noble nexus: a phosphino-phen ligand for tethering precious metals.

Controlled formation of mixed-metal bimetallics was achieved two derivatised 1,10-phenanthroline ligands bearing an imino- or amino-phosphine appendage at the 5-position. Selective coordination of the phen group to the [Re(CO)Cl] core was achieved enabling precise construction of bimetallic complexes with a second rhenium centre or with gold. The mixed Ru/Au complex was similarly obtained with the imino-phosphine but access to the heterobimetallic iridium systems required prior formation of the P-bound gold complexes subsequent to the introduction of the [Ir(Ppy)] fragment.

Welcoming Neighbour or Inhospitable Host? Selective Second Metal Binding in 5- and 6-Phospha-Substituted Bpy Ligands.

The controlled formation of mixed-metal bimetallics was realised through use of a -[Re(CO)(,'-bpy-P)Cl] complex bearing an exogenous 2,4,6-trioxa-1,3,5,7-tetramethyl-8-phosphaadamantane donor at the 5-position of the bpy. The introduction of gold, silver, and rhodium with appropriate secondary ligands was readily achieved from established starting materials. Restricted rotation about the C-P bond was observed in several of the bimetallic complexes and correlated with the relative steric bulk of the second metal moiety.

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-L)]BF1, has been used as the precursor for the formation of [AuAg(κ- ,κ-,'-1)](BF), 2a, [AuCu(κ- ,κ-,'-1)](BF), 2b and [AuAu'(κ-C,κ-N-1)](BF), 3.

Remote control: stereoselective coordination of electron-deficient 2,2'-bipyridine ligands to Re(I) and Ir(III) cores.

Highly diastereoselective coordination of unsymmetrical cationic 2,2'-bipyridine ligands bearing a chiral amidinium substituent to [Re(CO)Cl] and [Ir(PhPy)] cores is reported. Binding strength and stereoselectivity have been correlated with the position of the amidinium group on the bipy. The 4-, 5- and 6-substituted ligands all produce -[Re(CO)(LH)Cl]X selectively, while only the 4-derivative gives preferred formation of Δ-[Ir(Phpy)(4-LH)](BF).

Reactions promoted by hypervalent iodine reagents and boron Lewis acids.

Understanding the role of boranes in hypervalent iodine chemistry will open up new reactivities which can be utilised in organic synthesis. Due to similar reactivities, λ3-iodanes have presented themselves as viable alternatives for many transformations dominated by transition metals whilst mitigating some of the associated drawbacks of metal systems. As showcased by recent reports, boranes can adopt a dual role in hypervalent iodine chemistry that surpasses mere activation of the hypervalent iodine reagent.

Asymmetric ketone hydroboration catalyzed by alkali metal complexes derived from BINOL ligands.

The ability of alkali metal complexes featuring functionalized BINOL-derived ligands to catalyze ketone hydroboration reactions was explored. The reduced products were formed in excellent yields and with variable enantioselectivities dependent upon the nature of the ligand and the alkali metal cation.

Twisting the arm: structural constraints in bicyclic expanded-ring N-heterocyclic carbenes.

A series of diaryl, mono-aryl/alkyl and dialkyl mono- and bicyclic expanded-ring N-heterocyclic carbenes (ER-NHCs) have been prepared and their complexation to Au(i) investigated through the structural analysis of fifteen Au(NHC)X and/or [Au(NHC)]X complexes. The substituted diaryl 7-NHCs are the most sterically encumbered with large buried volume (%V) values of 40-50% with the less flexible six-membered analogues having %V values at least 5% smaller. Although the bicyclic systems containing fused 6- and 7-membered rings (6,7-NHCs) are constrained with relatively acute NCN bond angles, they have the largest %V values of the dialkyl derivatives reported here, a feature related to the fixed conformation of the heterocyclic rings and the compressional effect of a pre-set methyl substituent.

Halide and substituent dependent structural variation in copper(i) halide complexes of 1,5,9-triphosphacyclododecanes.

The reactions of 1,5,9-triethyl-1,5,9-triphosphacyclododecane, [12]-ane-P3Et3, and 1,5,9-tri(2-propyl)-1,5,9-triphosphacyclododecane, [12]-ane-P3iPr3 with copper(i)halides produce either bimetallic species of the type [([12]-ane-P3R3)Cu(CuX2)] (X = halide) or monomeric [([12]-ane-P3R3)CuX] depending on the nature of the halide and, to a lesser extent, the macrocycle. With CuCl only bimetallic complexes are formed with one copper centre bound to the macrocycle and a second attached through a Cu-Cu bond with a mono bridging chloride. CuBr affords monomeric [([12]-ane-P3R3)CuBr] complexes when performed in a 1 : 1 M : L ratio whereas the bimetallic compound [([12]-ane-P3Et3)(CuBr)2], resulted when a 2 : 1 ratio of M : L was employed.

Synthesis and photophysical properties of imine borane adducts towards vapochromic materials.

A series of alkynyl aryl conjugated aldehydes and imines were prepared and their adducts with various Lewis acidic boranes have been studied via NMR, absorption, and luminescence spectroscopies in solution. The imine-B(C6F5)3 adduct showed remarkable solution stability, and was then trialled in vapochromism experiments using simple impregnated paper strips to examine the fluorescence responses.

Asymmetric Cationic Phosphines: Synthesis, Coordination Chemistry, and Reactivity.

A single enantiomer of a cationic phosphine, [α-CgPAmHMe]BF, containing two asymmetric subunits, an amidinium group (AmH) and a phosphacycle (CgP), has been synthesized and isolated. The ligand, which is of an extremely rare class, has been coordinated to Rh(I), Au(I), Ag(I), Cu(I), and Pt(0) to enable an empirical assessment of its donor properties. Analysis of the IR stretching frequency of the carbonyl ligand in trans-[Rh(α-CgPAmHMe)(CO)Cl](BF) coupled with metric data obtained from crystal-state molecular structures of pertinent complexes confirms the strong π-accepting properties of the ligand.

Synthesis and characterisation of fluorescent aminophosphines and their coordination to gold(i).

Three novel fluorescent aminophosphine ligands have been synthesised that incorporate napthyl (L1), pyrenyl (L2) and anthraquinone (L3) chromophores into their structures. The ligands react with [AuCl(tht)] (tht = tetrahydrothiophene) to give neutral complexes of the form [AuCl(L1-3)]. Solid state, X-ray crystallographic data was obtained for the anthraquinone derivative, [AuCl(L3)], and showed a distorted linear coordination geometry at Au(i).

Ring-Expanded N-Heterocyclic Carbenes for Copper-Mediated Azide-Alkyne Click Cycloaddition Reactions.

A series of well-defined copper(I) complexes bearing ring-expanded N-heterocyclic carbene (NHC) ligands has been applied to the azide-alkyne cycloaddition reaction. The obtained results notably showed that the six-membered NHC ligands outperform well-established five-membered ones. [CuI(Mes-6)] displayed a remarkable catalytic activity while respecting the strict criteria for click reactions.

Push and pull: the potential role of boron in N activation.

Recent developments in main group chemistry towards the activation and conversion of N have lead to the revelation that boron can greatly affect these processes. Boron is capable of acting both as a borane Lewis acid to activate metal-N complexes and as an ambiphilic borylene able to activate free N. The latter example is capable of both accepting and donating electron density in a manner reminiscent of transition metal systems containing both filled and empty d-orbitals.

Amidine functionalized phosphines: tuneable ligands for transition metals.

Attachment of racemic 1,3,5,7-tetramethyl-2,4,6-trioxa-8-phosphatricyclo[3.3.1.

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.

Chiral carbene-borane adducts: precursors for borenium catalysts for asymmetric FLP hydrogenations.

The carbene derived from (1R,3S)-camphoric acid was used to prepare the borane adduct with Piers' borane 7. Subsequent hydride abstraction gave the borenium cation 8. Adducts with 9-BBN and the corresponding (1R,3S)-camphoric acid-derived carbene bearing increasingly sterically demanding N-substituents (R = Me 9, Et 10, i-Pr 11) and the corresponding borenium cations 12-14 were also prepared.

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.

Manganese(I) templates for the construction of benzannulated triphosphamacrocycles.

Nine-membered 1,4,7-triphosphamacrocycles with unsaturated benzo-backbones have been prepared using the [(CO)3Mn](+) unit as a template. Two synthetic methods have been employed for the macrocyclisation both of which involve the attack of a coordinated phosphide at an activated, electrophilic ortho-fluorophenyl substituent on a neighbouring pnictide donor. Addition of base to the precursor complex fac-[(CO)3Mn(dfppb)(PhPH2)](+), 1, where dfppb = 1,2-bis[di(2-fluorophenyl)phosphino]benzene, results in the direct formation of the macrocyclic compound fac-[Mn(CO)3(tribenzo-9aneP3-Ph,Ph(F)2)](+), 3.

Aspects of the coordination chemistry of rac-trans-1,2-diphosphinocyclohexane and the preparation of reinforced 9aneP₃ and 9anePN₂ macrocycles.

Racemic trans-1,2-diphosphinocyclohexane (t-chxnP2) has been synthesised and its coordination chemistry to Cu(I), Ag(I), Mn(I) and Fe(II) investigated. Compounds of empirical formula [Cu(t-chxnP2)2]BF4 and [Ag(t-chxnP2)2]BF4 have been prepared as isomeric mixtures and the solid-state structure of both complexes determined by single-crystal techniques. The Cu(I) complex is a monomeric species which crystallises with one ligand bearing the R,R configuration and the other being the S,S isomer whereas the Ag(I) complex crystallises as a polymer containing both chelating and bridging t-chxnP2 ligands with 3- and 4-coordinate Ag(I) centres and argentophilic bonds.

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.

Variable coordination of a chiral diphosphine containing an amidinium/NHC group within its backbone: μ-P,P', κ2-P,P' and κ3-P,C,P' coordination modes.

A diphosphine ligand (1·HPF(6)), which is a potential precursor to a PC(NHC)P pincer, with a backbone containing two phenylene groups and a central bicyclic 4-aza-2-azoniabicyclo[3.2.1]oct-2-ene unit has been synthesised and coordinated to Pd(II) and Pt(II) to give trans-[M(κ(2)-P,P'-)Cl(2)]PF(6) where M = Pd (2) or Pt (3a).

Monovalent chiral-at-copper complexes: halide-controlled diastereoselectivity.

An unusual example of diastereoselectivity has been observed in Cu(κ(3)-P,C,P'-1)X complexes where 1 is an asymmetric tridentate ligand containing a bicyclic NHC framework and X is a halide. When X is Cl(-), the S(Cu) isomer is formed selectively whereas when X = I(-) the R(Cu) diastereomer is preferred.

Iron(II) template synthesis of benzannulated triphospha- and triarsamacrocycles.

Nine-membered 1,4,7-triphospha- and triarsamacrocycles with unsaturated benzo-backbones have been prepared using the [Cp(R)Fe](+) unit as a template. The cyclisation involves the attack of a coordinated phosphide (or arsenide) nucleophile at an activated, electrophilic ortho-fluorophenyl substituent on a neighbouring pnictide donor. The macrocycle assembly is of the 2 + 1 type where two new chelate rings are formed from appropriately derivatised bidentate and monodentate phosphines/arsines.