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Using a diverse array of thermally robust phosphine enediyne ligands (dxpeb, X = Ph, Ph- p OCH 3 , Ph- p CF 3 , Ph- m 2 CH 3 , Ph- m 2 CF 3 , i Pr, Cy, and t Bu) a novel suite of cisplatin-like Pt(ii) metalloenediynes (3, Pt(dxpeb)Cl 2 ) has been synthesized and represents unique electronic perturbations on thermal Bergman cyclization kinetics. Complexes 3e (Ph- m 2 CF 3 ) and 3f ( i Pr) are the first of this structure type to be crystallographically characterized with inter alkyne termini distances (3e: 3.13 Å; 3f: 3.10 Å) at the lower end of the widely accepted critical distance range within which enediynes should demonstrate spontaneous ambient temperature cyclization. Despite different electronic profiles, these metalloenediynes adopt a rigid, uniform structure suggesting complexes of the form Pt(dxpeb)Cl 2 have orthogonalized geometric and electronic contributions to thermal Bergman cyclization. Kinetic activation parameters determined using 31 P NMR spectroscopy highlight the dramatic reactivity and thermal tunability of these complexes. At room temperature, the half-life ( t 1/2 ) of cyclization spans a range of ∼35 hours and for the aryl phosphine derivatives, cycloaromatization rates are 10-30 times faster for complexes with electron donating substituents (3b: Ph- p OCH 3 ; 3d: Ph- m 2 CH 3 ) compared to those with electron withdrawing substituents (3c: Ph- p CF 3 ; 3e: Ph- m 2 CF 3 ). Computational interrogation of the aryl phosphine metalloenediynes 3a-3e reveals that the origin of this precise electronic control derives from electronic withdrawing group-mediated alkyne carbon polarization that amplifies coulombic repulsion increasing the cyclization barrier height. Additionally, mixing between the in-plane π-orbitals and the phosphine aryl ring system is pronounced for complexes with electron donating substituents which stabilizes the developing C-C bond and lowers the activation barrier. This π-orbital mixing is negligible however, for complexes with electron withdrawing substituents due to an energetic mismatch of the orbital systems. Overall, this work demonstrates that for geometrically rigid frameworks, even remote enediyne functionalization can have pronounced effects on activation barrier., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

Supramolecular dimers are elementary units allowing the build-up of multi-molecule architectures. New among these are cyanostar-stabilized dimers of phosphate and phosphonate anions. While the anion dimerization at the heart of these assemblies is reliable, the covalent synthesis leading to this class of designer anions serves as a bottleneck in the pathway to supramolecular assemblies. Herein, we demonstrate the reliable synthesis of 14 diverse anionic monomers by Heck coupling between vinyl phosphonic acid and aryl bromide compounds. When this synthesis is combined with reliable anion dimerization, we show formation of supramolecular dimers and polymers by co-assembly with cyanostar macrocycles. The removal of the covalent bottleneck opened up a seamless synthetic route to iterate through three monomers affording the solubility needed to characterize the mechanism of supramolecular polymerization. We also test the idea that the small size of these vinyl phosphonates provide identical dimer stabilities across the library by showing how mixtures of anions undergo statistical (social) self-sorting. We exploit this property by preparing soluble copolymers from the mixing of different monomers. This multi-anion assembly shows the utility of a library for programming properties., Competing Interests: The authors declare no competing financial interests., (This journal is © The Royal Society of Chemistry.)

X-ray photoemission spectroscopy (XPS) has been used to examine the interaction between Au and HfS 3 at the Au/HfS 3 interface. XPS measurements reveal dissociative chemisorption of O 2 , leading to the formation of an oxide of Hf at the surface of HfS 3 . This surface hafnium oxide, along with the weakly chemisorbed molecular species, such as O 2 and H 2 O, are likely responsible for the observed p-type characteristics of HfS 3 reported elsewhere. HfS 3 devices exhibit n-type behaviour if measured in vacuum but turn p-type in air. Au thickness-dependent XPS measurements provide clear evidence of band bending as the S 2p and Hf 4f core-level peak binding energies for Au/HfS 3 are found to be shifted to higher binding energies. This band bending implies formation of a Schottky-barrier at the Au/HfS 3 interface, which explains the low measured charge carrier mobilities of HfS 3 -based devices. The transistor measurements presented herein also indicate the existence of a Schottky barrier, consistent with the XPS core-level binding energy shifts, and show that the bulk of HfS 3 is n-type.

The syntheses of (DIM)Ni(NO 3 ) 2 and (DIM)Ni(NO 2 ) 2 , where DIM is a 1,4-diazadiene bidentate donor, are reported to enable testing of bis boryl reduced N-heterocycles for their ability to carry out stepwise deoxygenation of coordinated nitrate and nitrite, forming O(Bpin) 2 . Single deoxygenation of (DIM)Ni(NO 2 ) 2 yields the tetrahedral complex (DIM)Ni(NO)(ONO), with a linear nitrosyl and κ 1 -ONO. Further deoxygenation of (DIM)Ni(NO)(ONO) results in the formation of dimeric [(DIM)Ni(NO)] 2 , where the dimer is linked through a Ni-Ni bond. The lost reduced nitrogen byproduct is shown to be N 2 O, indicating N-N bond formation in the course of the reaction. Isotopic labelling studies establish that the N-N bond of N 2 O is formed in a bimetallic Ni 2 intermediate and that the two nitrogen atoms of (DIM)Ni(NO)(ONO) become symmetry equivalent prior to N-N bond formation. The [(DIM)Ni(NO)] 2 dimer is susceptible to oxidation by AgX (X = NO 3 - , NO 2 - , and OTf - ) as well as nitric oxide, the latter of which undergoes nitric oxide disproportionation to yield N 2 O and (DIM)Ni(NO)(ONO). We show that the first step in the deoxygenation of (DIM)Ni(NO)(ONO) to liberate N 2 O is outer sphere electron transfer, providing insight into the organic reductants employed for deoxygenation. Lastly, we show that at elevated temperatures, deoxygenation is accompanied by loss of DIM to form either pyrazine or bipyridine bridged polymers, with retention of a BpinO - bridging ligand., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Amines are ubiquitous in the chemical industry and are present in a wide range of biological processes, motivating the development of amine-sensitive sensors. There are many turn-on amine sensors, however there are no examples of turn-on sensors that utilize the amine's ability to react by single electron transfer (SET). We investigated a new turn-on amine probe with a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) fluorophore. BODIPY fluorescence is first preprogrammed into an off state by internal photoinduced electron transfer (PET) to an electron-deficient quinolinium ring, resulting in fluorescence quenching. At low concentrations of aliphatic amine (0 to 10 mM), this PET pathway is shut down by external SET from the amine to the photoexcited charge-transfer state of the probe and the fluorescence is turned on. At high concentrations of amine (50 mM to 1 M), we observed collisional quenching of the BODIPY fluorescence. The probe is selective for aliphatic amines over aromatic amines, and aliphatic thiols or alcohols. The three molecular processes modulate the BODIPY fluorescence in a multi-mechanistic way with two of them producing a direct response to amine concentrations. The totality of the three molecular processes produced the first example of a multi-state and dose-responsive amine sensor.

The importance of phosphate in biology and chemistry has long motivated investigation of its recognition. Despite this interest, phosphate's facile oligomerization is only now being examined following the discovery of complexes of anion-anion dimers of hydroxyanions. Here we address how oligomerization dictates phosphate's recognition properties when engaged with planar cyanostar macrocycles that can also oligomerize by stacking. The crystal structure of cyanostar with phosphate shows an unprecedented tetrameric stack of cyanostar macrocycles threaded by a phosphate trimer, [H 2 PO 4 ···H 2 PO 4 ···H 2 PO 4 ] 3- . The solution behaviour, studied as a function of solvent quality, highlights how dimers and trimers of phosphate drive formation of higher order stacks of cyanostar into dimer, trimer and tetramer co-assemblies. Solution behaviors differ significantly from simpler complexes of bisulfate hydroxyanion dimers. Phosphate oligomerization is: (1) preferred over ion pairing with tetrabutylammonium cations, (2) inhibits disassembly of the complexes upon dilution, and (3) resists interference from competitive anion solvation. The phosphate oligomers also appear critical for stability; complexation of just one phosphate with cyanostars is unfavored. The cyanostar's ability to self-assemble is found to create a tubular, highly electropositive cavity that complements the size and shape of the phosphate oligomers as well as their higher charge. When given the opportunity, phosphate will cooperate with the receptor to form co-assembled architectures.

The behavior of the complex (H 2 L)CoCl 2 , where H 2 L is a bis-(pyrazol-3-yl)pyridine, towards Brønsted bases is studied, to evaluate peripheral NH deprotonation as a route to a dianionic pincer ligand on a d 7 center. Deprotonation is found to also remove chloride from cobalt, and the decreased metal coordination number is then satisfied by bimolecular reaction of the newly formed peripheral deprotonated pyrazolate nitrogen, leading to Co 2 units bridged by some of the pyrazolates, in the analogous species [Co 2 (L)(LH)] 2 (L) and [Co 2 (L)(HL)] 2 [Co(L) 2 ], but also occasionally by chloride retention, in LiCo 2 L 2 Cl. Reacting LiCo 2 L 2 Cl with tBuNC, yields monomeric LCo(tBuNC) 2 , shown to be a 17 valence electron species. Use of excess LiN(SiMe 3 ) 2 in deprotonation of (H 2 L)CoCl 2 leads to a product containing a Co[N(SiMe 3 ) 2 ] 2 substructure, which illustrates opening of the Co 2 L 2 dimer in response to an attacking nucleophile.

Bulky tris(carbene)borate ligands provide access to high spin iron(ii) phosphido complexes. The complex PhB(MesIm) 3 FeP(H)Ph is thermally unstable, and [PPh] group insertion into a C-H bond of the supporting ligand is observed. An arrested α-hydride migration mechanism suggests increased nucleophilicity of the phosphorus atom facilitates [PPh] group transfer reactivity.

Anion-templated rotaxanes are a rare class of functional organic molecules capable of novel switching and mechanical behaviors. Yet, investigations of these properties are limited by existing synthetic strategies. We show a high-yielding synthesis (80%) of [3]rotaxanes using shape-persistent macrocycles, cyanostars, and anionic organo-phosphate templates catalyzed by low steric-demand click chemistry. The reaction yields correlate with the template's binding affinities. Use of longer linkers relieves steric congestion to enable a reversible acid-base response, opening the way to molecular switching.

Structural, spectroscopic and magnetic methods have been used to characterize the tris(carbene)borate compound PhB(MesIm) 3 Mn≡N as a four-coordinate manganese(IV) complex with a low spin ( S = 1/2) configuration. The slow relaxation of the magnetization in this complex, i.e. its single-molecule magnet (SMM) properties, is revealed under an applied dc field. Multireference quantum mechanical calculations indicate that this SMM behavior originates from an anisotropic ground doublet stabilized by spin-orbit coupling. Consistent theoretical and experiment data show that the resulting magnetization dynamics in this system is dominated by ground state quantum tunneling, while its temperature dependence is influenced by Raman relaxation.

The size-dependent recognition of large anions by shape-persistent macrocycles is poorly understood. To address this shortcoming, we created a bulky cyanostar that only forms 1 : 1 complexes and show the affinities best follow the expectations of size matching but only when solvent bias is removed.

The easy-to-prepare Nb(V) aryloxide complex [(ArO)2Nb(μ-Cl)Cl2]2 (OAr = 2,6-bis(diphenylmethyl)-4-tert-butylphenoxide) is a precursor to both Nb(IV), [trans-(ArO)2NbCl2(THF)2], and Nb(III), K3[(ArO)4Nb2(μ-Cl)3Cl2], molecules. The Nb(IV) and (V) complexes readily split atmospheric nitrogen at room temperature and 1 atmosphere, under reducing conditions, to produce the low-coordinate nitride dimer [(ArO)2Nb(μ-N)]2 and its radical anion, K[(ArO)2Nb(μ-N)]2.

Complex (PNP)Ti=CH(t)Bu(CH(2)(t)Bu) (PNP(-) = N[2-P(CHMe(2))(2)-4-methylphenyl](2)) eliminates H(3)C(t)Bu to form transient (PNP)Ti≡C(t)Bu, which activates the C-F bond of ortho-difluoropyridine and ortho-fluoropyridine to form the alkylidene-fluoride complexes, (PNP)Ti=C[(t)Bu(NC(5)H(3)F)](F) (1) and (PNP)Ti=C[(t)Bu(NC(5)H(4))](F) (2), respectively. When (PNP)Ti=CH(t)Bu(CH(2)(t)Bu) is treated with meta-fluoropyridine, the ring-opened product (PNP)Ti(C((t)Bu)CC(4)H(3)-3-FNH) (3) is the only recognizable titanium metal complex formed. Theoretical studies reveal that pyridine binding disfavors 1,2-CF bond addition across the alkylidyne ligand in the case of ortho-fluoride pyridines, while sequential [2 + 2]-cycloaddition/β-fluoride elimination is a lower energy pathway. In the case of meta-fluoropyridine, [2 + 2]-cycloaddition and subsequent ring-opening metathesis is favored as opposed to C-H bond addition or sequential [2 + 2]-cycloaddition/β-hydride elimination. In all cases, C-H bond addition of ortho-fluoropyridines or meta-fluoropyridine is discouraged because such substrate must bind to titanium via its C-H bond, which is rather weak compared to the titanium-pyridine binding.

Thermal Bergman cyclization of Pt(II) dialkynylporphyrins reveals a marked reduction in the cyclization temperature relative to the free base and Zn(II) derivatives. In contrast, photogenerated (3)ππ* population produces no detectable Bergman photocyclization, suggesting that the photoreactivities of the related free base and Zn(II) derivatives occurs via the (1)ππ* state.

Reduction of the dinuclear Co(II) nindigo complex dmp(2)Nin[Co(N{SiMe(3)}(2))](2), with 1 or 2 equiv. of K(0) (or KC(8)), affords the reduced complexes [dmp(2)Nin{Co(N{SiMe(3)}(2))}(2)](-) and [dmp(2)Nin{Co(N{SiMe(3)}(2))}(2)](2-), respectively. Inspection of these reduced species reveals ligand-centered reduction, with each cobalt ion retaining a formal 2+ oxidation state.

The synthesis and characterization of a series of iridium(I) and iridium(III) complexes supported by a 3,5-bis(trifluoromethyl)-2-(2'-pyridyl)pyrrole (L(-)) ligand are reported. Compound [Ir(L)(COD)] (COD = 1,5-cyclooctadiene) demonstrates reversible binding of hydrogen to form a dihydride complex [Ir(L)(H)(2)(COD)] with no hydrogenation of COD.

Treatment of d(1) [(nacnac)TiCl(Ntol(2))] with NaN(3) results in NaCl formation and N(2) ejection to yield the first four coordinate, parent imide [(nacnac)Ti=NH(Ntol(2))] (nacnac(-)=[ArNC(CH(3))](2)CH, Ar = 2,6-iPr(2)C(6)H(3), tol = 4-CH(3)C(6)H(4))., (This journal is © The Royal Society of Chemistry 2012)

The addition of 2,6-dimethylphenyl isocyanide (CN[DMeP], two equivalents) to previously reported (PNP)Sc(III) pyridyl complexes resulted in the formation of novel indoline complexes of scandium. By varying the nature of the pyridyl moiety one can intercept an intermediate prior to methyl migration. In addition to structural studies of two indolene complexes, we also propose a mechanism for the insertion and indolene ring closure., (This journal is © The Royal Society of Chemistry 2011)

An intimate interplay of O-H···O/C-H···F hydrogen bonds and π-π stacking interactions allows a phenyleneethynylene-based dendritic molecule to fold and self-assemble into two distinctively different molecular crystals as pseudopolymorphs.

Mononuclear nickel and cobalt boryl complexes have been prepared via sigma-bond metathesis reactions and in the case of nickel, an intermediate comprised of a Lewis acid-base type adduct has been experimentally detected by (31)P NMR spectroscopy and its structure probed by DFT calculations.

Species (PNP)Ir(X)(Y), where PNP = N(SiMe(2)CH(2)P(t)Bu(2))(2)(-1) with X and Y halide, have a (t)Bu group C-H bond heterolytically split by addition across the Ir-N bond.

The phosphanylidene-sigma(4)-phosphorane reagents Me(3)P[double bond, length as m-dash]PAr (Ar = 2,4,6-(t)Bu(3)C(6)H(2) and 2,6-Mes(2)C(6)H(3)) are good delivery vehicles of the terminal phosphinidene moiety, PAr, to early-transition metals composed of zirconium and vanadium.

Zinc reduction of [(Cym)RuCl(2)](2) gives [(Cym)RuCl](2), (Cym = 1,4-Me(i)PrC(6)H(4)), whose reactivity is evaluated. This Ru(I) dimer with two bridging chlorides shows no reactivity towards H(2), N(2), N(2)O or methyl triflate, but does add HCl to form (Cym)(2)Ru(2)HCl(3). Attempts to form a monomeric monovalent ruthenium complex with dppm, Ph(2)PCH(2)PPh(2), gives disproportionation to (Cym)RuCl(2)(eta(1)-dppm) and (Cym)Ru(eta(2)-dppm). With terpyridyl, the analogous disproportionation behavior is observed, to form Ru(terpy)(2)(2+) and a zero valent product, which decomposed before it could be isolated. The molecular orbitals, from a DFT calculation, of [(Cym)RuCl](2) show the LUMO to be in a sterically crowded region of the molecule, and thus helps to account for the reactivity targeted for small and more nucleophilic reagents, while the HOMO is accessible to reaction with HCl.

The reaction of (PNP)NiH, where PNP is ((t)Bu2PCH2SiMe2)2-N(-1), with CO2 occurs over a period of hours at 25 degrees C to form (POP)NiH(NCO), which involves transposition of the initial amide nitrogen and one oxygen of CO2.

A conformationally pre-organized ligand platform allows for restricted swivelling motions of two aryleneethynylene-appended 2,2'-bipyridyl units that function as a tight bischelator as well as a ratiometric fluorescence sensor for selected metal ions.

Highly diastereo- and enantioselective additions of alpha-nitrophosphonates to imines catalyzed by a chiral Brønsted acid are described.

Reaction of 2,3-dioxochlorins with benzeneselenic anhydride (BSA) results in the formation of unusual ring-contracted azetine derivatives that further react with BSA to afford porpholactones.

Tetradentate metalloenediynes with strong imine and weaker thioether coordination serve as a geometrically non-rigid switch to drive thermal Bergman cyclization.

The air and moisture stable rhodium N-heterocyclic carbene (NHC) complex, RhCl(IMes)(COD)(IMes =N,N[prime or minute]-bis(2,4,6-trimethylphenyl)imidazole-2-ylidine; COD = 1,5-cyclooctadiene), facilitates a diastereoselective metal-catalyzed [4 + 2 + 2] carbocyclization of 1,6-enynes in the presence of silver triflate and 1,3-butadiene.

Alcoholysis of [Fe6O2(OH)2(O2CBut)10(hep)2] (1) affords ferric wheels of different nuclearities: methanol yields [Fe10(OMe)20(O2CBut)10], whereas phenol gives the structurally unprecedented wheel [Fe8(OH)4(OPh)8(O2CBut)12], and the first to contain phenoxide.

Conformationally constrained ethylene-diamine metalloenediyne compounds exhibit alkyne termini separations that are constant and independent of metal center geometry. Ancillary chloride ligand electron donation into the Bergman cyclization reaction coordinate, however, dramatically influences the observed temperatures.

Computations employing density functional theory on the reactions between ethyne and the model compounds (HE)3M identical to M(EH)3, where M = Mo and W and E = O and S, predict that the alkyne adducts M2(mu-C2H2)(EH)6 are thermodynamically favored with respect to the metathesis products HC identical to M(EH)3 except when M = W and E = O; the reaction between (tBuO)3 W identical to CPh and 2-MeC6H4SH (> 3 equiv.) yields W2(mu-PhCCPh)(SC6H4-2-Me)6 consistent with expectations based on the calculations.

The 3 MnIV title compound has been prepared and characterized by X-ray crystallography and magnetochemistry; the complex contains a [Mn(mu-O)2Mn(mu-O)2Mn]4+ core and possesses an S = 3/2 ground state.