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Boraadamantanes are a privileged class of caged group 13 compounds having a trigonal pyramidal (non-VSEPR) ground-state. The Lewis acid–base chemistry of this type of compound is underdeveloped when compared to acyclic derivatives. This report provides the first examples of bifunctional boraadamantanes with an appended phosphine moiety (also the first boraadamantanes having a phosphorus–boron bond). Using this scaffold, boraadamantane coordination compounds are accessed for the first time. [ABSTRACT FROM AUTHOR]

Coordinatively unsaturated transition-metal compounds stabilized by supplemental electron donation from π-basic ligands are described as "operationally unsaturated". Such complexes are useful analogues of active catalyst structures that readily react with substrate molecules. We report that [Ph2P(C6H4)NCHC(CH3)2]− (L1) effectively stabilizes Ru(II) in an operationally unsaturated form. In the absence of Lewis bases, the 1-azaallyl group of L1 dominantly coordinates through a κ1-N mode, but can readily and reversibly isomerize to an η3-NCC coordination mode to stabilize the metal. As an operationally unsaturated complex, Ru(Cp*)(L1) dimerizes at low temperature. At ambient temperature it rapidly reacts with pyridine or PPh3 to form an adduct. These findings with L1 demonstrate that changes in the hapticity of a 1-azaallyl fragment offer an alternative means to stabilize low-coordinate metals. [ABSTRACT FROM AUTHOR]

Carbon–carbon coupling is one of the most powerful tools in the organic synthesis arsenal. Known methodologies primarily exploit monometallic Pd0/PdII catalytic mechanisms to give new C–C bonds. Bimetallic C–C coupling mechanisms that involve a PdI/PdII redox cycle, remain underexplored. Thus, a detailed mechnaistic understanding is imperative for the development of new bimetallic catalysts. Previously, a PdII–Me dimer (1) supported by L1, which has phosphine and 1-azaallyl donor groups, underwent reductive elimination to give ethane, a PdI dimer, a PdII monometallic complex, and Pd black. Herein, a comprehensive experimental and computational study of the reactivity of 1 is presented, which reveals that the versatile coordination chemistry of L1 promotes bimetallic C–C bond formation. The phosphine 1-azaallyl ligand adopts various bridging modes to maintain the bimetallic structure throughout the C–C bond forming mechanism, which involves intramolecular methyl transfer and 1,1-reductive elimination from one of the palladium atoms. The minor byproduct, methane, likely forms through a monometallic intermediate that is sensitive to solvent C–H activation. Overall, the capacity of L1 to adopt different coordination modes promotes the bimetallic C–C coupling channel through pathways that are unattainable with statically-coordinated ligands. [ABSTRACT FROM AUTHOR]

The synthesis of a variety of bis(catecholato)germanes is reported. The Lewis acidity of the bis(catecholato)germanes was assessed using the experimental Gutmann–Beckett method and computational FIA and GEI methods. The oligomerization of alkenes using bis(catecholato)germanes demonstrates the use of these complexes in catalysis. The use of donor additives in the dimerization of α-methylstyrene resulted in selectivity control comparable to transition metal catalyst systems. [ABSTRACT FROM AUTHOR]

Lewis acids are highly sought after for their applications in sensing, small-molecule activation, and catalysis. When combined with π-conjugated molecular frameworks, Lewis acids with unique optoelectronic properties can be realized. Here, we use a tridentate formazanate ligand to create a planar, redox-active, fluorescent, and strongly Lewis-acidic borenium cation. We also demonstrate that this compound can act as a colourimetric probe for reactivity. [ABSTRACT FROM AUTHOR]

A new di-2-pyridylamine ligand with an appended azobenzene group (2-C5H4N)2N-4-C6H4-N＝N-Ph, dpaa, is reported. This ligand readily forms the platinum(II) complexes [PtMe2(dpaa)], 1, and [PtCl2(dpaa)], 2. Complex 1 is electron-rich and it undergoes oxidative addition with I2, MeI or PhCH2Br to give the corresponding organoplatinum(IV) complexes [PtI2Me2(dpaa)], [PtIMe3(dpaa)] or [PtBrMe2(CH2Ph)(dpaa)]. Both the ligand dpaa and its platinum complexes undergo photoswitching by trans–cis isomerization about the N＝N linkage. [ABSTRACT FROM AUTHOR]

A new paramagnetic ligand, betaDTDA, and its coordination complex with Fe(hfac)2 are reported (betaDTDA = 4-(benzothiazol-2′-yl)-1,2,3,5-dithiadiazolyl; hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato-). The neutral radical betaDTDA is the first dithiadiazolyl ligand designed to include an electropositive sulphur moiety outside the thiazyl heterocycle, increasing the capacity for supramolecular, structure-directing electrostatic contacts and enabling new pathways for magnetic exchange. The Fe(hfac)2(betaDTDA) complex is composed of a hs-Fe(ii) center with the three bidentate ligands arranged about the ion in a distorted octahedral 6-coordinate environment. The magnetic properties of crystalline Fe(hfac)2(betaDTDA) are consistent with strong antiferromagnetic (AF) coupling between the metal and ligand moments, giving rise to a well-defined Stotal = 3/2 ground state that is the only thermally populated state below 40 K. Below 4 K, this complex exhibits slow relaxation of the magnetization detected by ac susceptibility measurements consistent with a single-molecule magnet (SMM) behaviour. [ABSTRACT FROM AUTHOR]

Several platinum(ii) complexes with ligands containing azo groups have been prepared and structurally characterised, and their photoswitching between trans and cis azo group isomers has been studied. The azo groups in the cationic complexes [PtMe(bipy)(4-NC5H4-N=N-4-C6H4X)][PF6], X = H, OH or NMe2, and in the dicationic complex [Pt(bipy)(4-H2NC6H4-N=N-C6H5)2][OTf]2 undergo trans to cis photoswitching on irradiation at 365 nm. The complex [PtMe(bipy)(4-NC5H4-N=N-4-C6H4NMe)2][PF6] also exhibits a reversible halochromic effect on protonation to give the dicationic complex [PtMe(bipy)(4-NC5H4-NH=N-4-C6H4NMe2]2+. The nature of the frontier orbitals in the platinum(ii) complexes depends on the charge on the complex and on the degree of metal–ligand π-bonding. [ABSTRACT FROM AUTHOR]

A series of novel cationic Re(iii) complexes [(DAAm)Re(CO)(NCCH3)2][X] [DAAm = N,N-bis(2-arylaminoethyl)methylamine; aryl = C6F5 (a), Mes (b)] [X = OTf (2), BArF4 [BArF4 = tetrakis[3,5-(trifluoromethyl)phenyl]borate] (3), BF4 (4), PF6 (5)], and their analogue [(DAmA)Re(CO)(Cl)2] [DAmA = N,N-bis(2-arylamineethyl)methylamino; aryl = C6F5] (6) were synthesized. The catalytic efficiency for the hydrosilylation reaction of aldehydes using 4a (0.03 mol%) has been demonstrated to be significantly more active than rhenium catalysts previously reported in the literature. The data suggest that electron-withdrawing substituents at the diamido amine ligand increase the catalytic efficiency of the complexes. Excellent yields were achieved at ambient temperature under neat conditions using dimethylphenylsilane. The reaction affords TONs of up to 9200 and a TOF of up to 126 h−1. Kinetic and mechanistic studies were performed, and the data suggest that the reaction is via a non-hydride ionic hydrosilylation mechanism. [ABSTRACT FROM AUTHOR]

The combination of a palladium(ii) precursor with a diimine–phenol ligand and an oxidant (H2O2 or O2) under different conditions has, serendipitously, given both a molecular square and a molecular tetrahedron by self-assembly of building blocks comprising palladium(ii) centres coordinated to the oxidised forms of the ligand. [ABSTRACT FROM AUTHOR]

The addition of an alkynyl cyclopropyl mechanistic probe to a digermyne did not lead to any ring-opened rearrangement products indicating that the reaction pathway does not involve any vinylic radicals or cations and providing experimental insight into the addition of alkynes to digermynes. [ABSTRACT FROM AUTHOR]

Two dimeric boron complexes of potentially tetradentate and trianionic β-diketiminate ligands bearing phenol substituents were prepared and characterized. The synthetic routes employed were designed to circumvent the undesirable formation of β-ketimines and 2-methylbenzoxazoles observed when traditional synthetic routes toward the target β-diketiminate ligands were attempted. The title complexes were isolated via demethylation of β-diketimine ligands and boron difluoride complexes bearing 2-anisole N-aryl substituents using boron tribromide. The resulting complexes were found to contain a unique hydrogen-bond-supported boron-oxygen-boron bridge, as confirmed by X-ray crystallography. The stability of the resulting dimeric structures relative to the corresponding monomeric, tetradentate boron complexes was studied computationally, and theory confirmed that the dimeric structures were strongly favored. The absorption spectra of the dimers were red-shifted relative to the parent β-diketimine ligands. The complexes were irreversibly oxidized and reduced electrochemically and were weakly emissive at low concentrations (Stokes shifts between 23 and 31 nm), showing little solvent dependence. [ABSTRACT FROM AUTHOR]

The complex [PtMe2({κ2-N,N-RN=CH-2-C5H4N})] reacts with oxygen in acetone solution to give the platinum(iv) complex [Pt(OH)Me2{κ3-N,N,O-RNH–CH(2-C5H4N)(CH=CMeO)}], when R = 2-C6H4OH, but not when R = Ph. It has been suggested that the phenol substituent plays two key biomimetic roles; firstly, in proton coupled electron transfer reactions in the activation of oxygen and hydroperoxide groups and, secondly, in proton relay from a methyl group of the coordinated acetone. [ABSTRACT FROM AUTHOR]

The reagents 1,2-C6H4(CH=NR)(SMe), R = CH2CH2NMe2 or Ph, react with [Pt2Me4(μ-SMe2)2] by oxidative addition of the aryl–sulfur bond to give the corresponding crystalline binuclear platinum(iv) compounds [Pt2Me4(μ-SMe)2(κ2-C,N-C6H4-2-CH=NR)2], as the isomers with Ci (R = CH2CH2NMe2 or Ph) or C1 (R = Ph) symmetry. These first examples of C–S bond activation at platinum(ii) occur easily at room temperature, and the reactions give complex equilibria of isomeric products, from which the isolated compounds crystallise. [ABSTRACT FROM AUTHOR]

Coordinatively unsaturated transition-metal compounds stabilized by supplemental electron donation from π-basic ligands are described as "operationally unsaturated". Such complexes are useful analogues of active catalyst structures that readily react with substrate molecules. We report that [Ph 2 P(C 6 H 4 )NCHC(CH 3 ) 2 ] - (L1) effectively stabilizes Ru(II) in an operationally unsaturated form. In the absence of Lewis bases, the 1-azaallyl group of L1 dominantly coordinates through a κ 1 -N mode, but can readily and reversibly isomerize to an η 3 -NCC coordination mode to stabilize the metal. As an operationally unsaturated complex, Ru(Cp*)(L1) dimerizes at low temperature. At ambient temperature it rapidly reacts with pyridine or PPh 3 to form an adduct. These findings with L1 demonstrate that changes in the hapticity of a 1-azaallyl fragment offer an alternative means to stabilize low-coordinate metals.

Carbon-carbon coupling is one of the most powerful tools in the organic synthesis arsenal. Known methodologies primarily exploit monometallic Pd 0 /Pd II catalytic mechanisms to give new C-C bonds. Bimetallic C-C coupling mechanisms that involve a Pd I /Pd II redox cycle, remain underexplored. Thus, a detailed mechnaistic understanding is imperative for the development of new bimetallic catalysts. Previously, a Pd II -Me dimer (1) supported by L1, which has phosphine and 1-azaallyl donor groups, underwent reductive elimination to give ethane, a Pd I dimer, a Pd II monometallic complex, and Pd black. Herein, a comprehensive experimental and computational study of the reactivity of 1 is presented, which reveals that the versatile coordination chemistry of L1 promotes bimetallic C-C bond formation. The phosphine 1-azaallyl ligand adopts various bridging modes to maintain the bimetallic structure throughout the C-C bond forming mechanism, which involves intramolecular methyl transfer and 1,1-reductive elimination from one of the palladium atoms. The minor byproduct, methane, likely forms through a monometallic intermediate that is sensitive to solvent C-H activation. Overall, the capacity of L1 to adopt different coordination modes promotes the bimetallic C-C coupling channel through pathways that are unattainable with statically-coordinated ligands.

The synthesis of a variety of bis(catecholato)germanes is reported. The Lewis acidity of the bis(catecholato)germanes was assessed using the experimental Gutmann-Beckett method and computational FIA and GEI methods. The oligomerization of alkenes using bis(catecholato)germanes demonstrates the use of these complexes in catalysis. The use of donor additives in the dimerization of α-methylstyrene resulted in selectivity control comparable to transition metal catalyst systems.

A new paramagnetic ligand, betaDTDA, and its coordination complex with Fe(hfac)2 are reported (betaDTDA = 4-(benzothiazol-2'-yl)-1,2,3,5-dithiadiazolyl; hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato-). The neutral radical betaDTDA is the first dithiadiazolyl ligand designed to include an electropositive sulphur moiety outside the thiazyl heterocycle, increasing the capacity for supramolecular, structure-directing electrostatic contacts and enabling new pathways for magnetic exchange. The Fe(hfac)2(betaDTDA) complex is composed of a hs-Fe(ii) center with the three bidentate ligands arranged about the ion in a distorted octahedral 6-coordinate environment. The magnetic properties of crystalline Fe(hfac)2(betaDTDA) are consistent with strong antiferromagnetic (AF) coupling between the metal and ligand moments, giving rise to a well-defined Stotal = 3/2 ground state that is the only thermally populated state below 40 K. Below 4 K, this complex exhibits slow relaxation of the magnetization detected by ac susceptibility measurements consistent with a single-molecule magnet (SMM) behaviour.

Several platinum(ii) complexes with ligands containing azo groups have been prepared and structurally characterised, and their photoswitching between trans and cis azo group isomers has been studied. The azo groups in the cationic complexes [PtMe(bipy)(4-NC 5 H 4 -N[double bond, length as m-dash]N-4-C 6 H 4 X)][PF 6 ], X = H, OH or NMe 2 , and in the dicationic complex [Pt(bipy)(4-H 2 NC 6 H 4 -N[double bond, length as m-dash]N-C 6 H 5 ) 2 ][OTf] 2 undergo trans to cis photoswitching on irradiation at 365 nm. The complex [PtMe(bipy)(4-NC 5 H 4 -N[double bond, length as m-dash]N-4-C 6 H 4 NMe) 2 ][PF 6 ] also exhibits a reversible halochromic effect on protonation to give the dicationic complex [PtMe(bipy)(4-NC 5 H 4 -NH[double bond, length as m-dash]N-4-C 6 H 4 NMe 2 ] 2+ . The nature of the frontier orbitals in the platinum(ii) complexes depends on the charge on the complex and on the degree of metal-ligand π-bonding.

A series of novel cationic Re(iii) complexes [(DAAm)Re(CO)(NCCH 3 ) 2 ][X] [DAAm = N,N-bis(2-arylaminoethyl)methylamine; aryl = C 6 F 5 (a), Mes (b)] [X = OTf (2), BAr F 4 [BAr F 4 = tetrakis[3,5-(trifluoromethyl)phenyl]borate] (3), BF 4 (4), PF 6 (5)], and their analogue [(DAmA)Re(CO)(Cl) 2 ] [DAmA = N,N-bis(2-arylamineethyl)methylamino; aryl = C 6 F 5 ] (6) were synthesized. The catalytic efficiency for the hydrosilylation reaction of aldehydes using 4a (0.03 mol%) has been demonstrated to be significantly more active than rhenium catalysts previously reported in the literature. The data suggest that electron-withdrawing substituents at the diamido amine ligand increase the catalytic efficiency of the complexes. Excellent yields were achieved at ambient temperature under neat conditions using dimethylphenylsilane. The reaction affords TONs of up to 9200 and a TOF of up to 126 h -1 . Kinetic and mechanistic studies were performed, and the data suggest that the reaction is via a non-hydride ionic hydrosilylation mechanism.

The addition of an alkynyl cyclopropyl mechanistic probe to a digermyne did not lead to any ring-opened rearrangement products indicating that the reaction pathway does not involve any vinylic radicals or cations and providing experimental insight into the addition of alkynes to digermynes.

Two dimeric boron complexes of potentially tetradentate and trianionic β-diketiminate ligands bearing phenol substituents were prepared and characterized. The synthetic routes employed were designed to circumvent the undesirable formation of β-ketimines and 2-methylbenzoxazoles observed when traditional synthetic routes toward the target β-diketiminate ligands were attempted. The title complexes were isolated via demethylation of β-diketimine ligands and boron difluoride complexes bearing 2-anisole N-aryl substituents using boron tribromide. The resulting complexes were found to contain a unique hydrogen-bond-supported boron-oxygen-boron bridge, as confirmed by X-ray crystallography. The stability of the resulting dimeric structures relative to the corresponding monomeric, tetradentate boron complexes was studied computationally, and theory confirmed that the dimeric structures were strongly favored. The absorption spectra of the dimers were red-shifted relative to the parent β-diketimine ligands. The complexes were irreversibly oxidized and reduced electrochemically and were weakly emissive at low concentrations (Stokes shifts between 23 and 31 nm), showing little solvent dependence.

The detailed syntheses of complexes 1-4, Re(O)(X)(DAP) (X = Me, 1; Cl, 2; I, 3; OTf (triflate), 4) incorporating the diamido pyridine (DAP) ancillary ligand (2,6-bis((mesitylamino)methyl)pyridine) are described and shown to be effective catalysts for oxygen atom transfer (OAT) reactions of PyO to PPh(3). The catalytic activities are as follows: 4≈3 > 2 > 1. The observed electronic trend is consistent with the turnover limiting reduction of the proposed Re(VII) dioxo intermediate, Re(O)(2)(X)(DAP), during the catalytic cycle. The catalytic activity of complexes 1-3 was compared to previously published diamido amine (DAAm) oxorhenium complexes of the type Re(O)(X)(DAAm) (X = Me, 5; Cl, 6; I, 7 and DAAm = N,N-bis(2-arylaminoethyl)methylamine) which exhibit hydrolytic degradation during the catalytic reaction. Complexes 1-3 displayed higher turnover frequencies compared to 5-7. This higher catalytic activity was attributed to the more rigid DAP ligand backbone, which makes the complexes less susceptible to decomposition. However, another decomposition pathway was proposed for this catalytic system due to the observation of Re(O)(3)((MesNCH(2))(MesNCH)NC(5)H(3)) 8 in which one arm of the DAP ligand is oxidized.