Synthesis and coordinating ability of an anionic cobaltabisdicarbollide ligand geometrically analogous to BINAP

The anionic chelating ligand [1,1'-(PPh2)2-3,3'-Co(1,2-C2B9H10)2]- has been synthesized from [3,3'-Co(1,2-C2B9H11)2]- in very good yield in a one-pot process with an easy work-up procedure. The coordinating ability of this ligand has been studied with Group 11 metal ions (Ag, Au) and with transition-metal ions (Pd, Rh). The two dicarbollide halves of the [1,1'-(PPh2)2-3,3'-Co(1,2-C2B9H10)2]- ligand can swing about one axis in a manner analogous to the constituent parts of BINAP and ferrocenyl phosphine derivatives. All these ligands function as hinges, with the most important property in relation to the coordination requirements of the metal being the PP distance. [1,1'-(PPh2)2-3,3'-Co(1,2-C2B9H10)2]-, BINAP, ferrocenyl phosphine derivatives, and other hinge ligands present a range of different PP separations, and consequently different coordination spheres and dispositions around metal cations. To account for these differences, the equation Dphi2 = D02 + 4 R2cos2(90-phi/2) has been developed. It relates the PP distance (Dphi) in a complex with the minimum PP distance (D0) that is characteristic of the hinge-type ligand.     

Formation of bridging alkene and conjugated dialkenes exclusively generated from alkynes on the [3,3'-Co(1,2-C2B9H11)2]- platform. The unique hydroboration role of [3,3'-Co(1,2-C2B9H11)2]-

The unprecedented metal-mediated transformation of an alkyne into a B,B' bridging alkene is reported. Also, the unprecedented synthesis of a conjugated dialkene derivative of [3,3'-Co(1,2-C2B9H11)2]- generated only from an alkyne, contrary to the usual case where an alkyne and an alkene are needed, is described. This has been possible through the singular capacity of a B-H to produce hydroboration.     

Aurophilicity-coordination interplay in the design of cyano-bridged nickel(II)-Gold(I) bimetallic assemblies: structural and computational studies of the gold(I)-gold(I) interactions

Two polymorphic cyano-bridged Au(I)-Ni(II) bimetallic complexes of formulas [Ni(en)2Au(CN)2][Au(CN)2] (1) and [Ni(en)2[Au(CN)2]2] (2) have been prepared from the 1:2 reaction between [Au(CN)2]- and either [Ni(en)2Cl2]Cl or [Ni(en)3]Cl2.2H2O, respectively. The structure of 1 consists of polymeric cationic chains of alternating [Au(CN)2]- and [Ni(en)2]2+ units running along the a axis and [Au(CN)2]- anions lying between the chains. The noncoordinated dicyanoaurate anions are aligned perpendicular to the ac plane and involved in aurophilic interactions with the bridging dicyanoaurate groups, ultimately leading to a 2D bimetallic grid. The structure of 2 consists of trinuclear molecules made of two [Au(CN)2]- anions linked to [Ni(en)2]2+ unit in trans configuration. Trinuclear units are joined by aurophilic interactions to form 1D zigzag chains. The magnetic properties of these compounds are strongly dominated by the local anisotropy of the octahedral Ni(II) ions, thus indicating that the magnetic exchange interaction mediated by dicyanoaurate bridging groups, if it exists, is very weak. To get insight into the electronic properties of the inter- and intramolecular interactions of the [Au(CN)2]- building blocks, the structures of different aggregates of dicyanogold units were optimized and then analyzed by making use of atoms-in-molecules (AIM) theory. Moreover, bond indices were calculated by methods based upon nonlinear population analysis.     

Diferratricarbaboranes of the subcloso-[(eta5-C5H5)2Fe2C3B8H11] type, the first representatives of the 13-vertex dimetallatricarbaborane series

Treatment of the [2-Cp-9-tBuNH-closo-2,1,7,9-FeC(3)B(8)H(10)] (1) ferratricarbollide (Cp = eta(5)-C(5)H(5) (-)) with Na(+) C(10)H(8) (-) in 1,2-dimethoxyethane (DME) at room temperature produced an air-sensitive transient anion with a tentatively identified nido-[tBuNH-CpFeC(3)B(8)H(10)](2-) constitution. In-situ reaction of this low-stability ion with [CpFe(CO)(2)I] or [CpFe(CO)(2)](2) generated three violet diferratricarbaboranes identified as paramagnetic subcloso complexes [4,5-Cp(2-)-4,5,1,6,7-Fe(2)C(3)B(8)H(11)] (2; yield 2 %), [4,5-Cp(2-)-4,5,1,7,12-Fe(2)C(3)B(8)H(11)] (3; yield 2 %), and [7-tBuNH-4,5-Cp(2-)-4,5,1,7,12-Fe(2)C(3)B(8)H(10)] (4; yield 14 %). These first representatives of the 13-vertex dimetallatricarbaborane family were characterized by EPR and IR spectroscopy, and mass spectrometry, and their structures were determined by X-ray diffraction analysis.     

Neutral nido-heteroboranes with non ionisable hydrogen as arenes in coordination

Designed ligands have been synthesised to produce the first arene-like metallacarborane. For arene-like coordination the number of electronegative elements on the coordinating site must be kept to a minimum. Choosing ligands with bulky substituents on the heteroatom allows easy rearrangement and arene-like coordination. This is more hampered the higher the number of hetereoatoms to be re-located.     

Influence of the solvent and R groups on the structure of (carboranyl)R2PI2 compounds in solution. Crystal structure of the first iodophosphonium salt incorporating the anion [7,8-nido-C2B9H10]-

The influence of the electron-donor or electron-acceptor capacity of the R groups (R = (i)Pr, Ph, Et) and the solvent on the molecular geometry in solution of adducts of carboranylphosphanes [(carboranyl)(i)Pr2P, (carboranyl)Ph2P and (carboranyl)Et2P] with I2 in 1 : 1 ratios, has been studied in detail by 31P{1H} and 11B{1H} NMR spectroscopies. The more electron-accepting Ph groups make the (carboranyl)Ph2P less nucleophilic, thus stabilizing the I2 encapsulated neutral biscarboranylphosphane-diiodine adducts in solution, such as (carboranyl)Ph2PI-IPPh2(carboranyl), generating P---I-I---P motifs. Even in a polar solvent, such as EtOH, the arrangement is preserved. The expected basicity of these carboranylphosphanes is: (carboranyl)(i)Pr2P > (carboranyl)Et2P > (carboranyl)Ph2P. Thus, the comparatively higher basicity of (carboranyl)Et2P vs. (carboranyl)Ph(2)P facilitates a higher transfer of electron density to the I2 sigma*, generating the ionic species, [(carboranyl)Et2PI]+I-, even in low polar solvents, such as CH2Cl2 and toluene, with no degradation of the cluster. However, in EtOH, the formation of the anionic [7,8-nido-C2B(9)H10]- cluster takes place by removal of one boron atom from the closo cluster. The basicity of (carboranyl)(i)Pr(2)P should be the highest, superior to (carboranyl)Et2P. This is observed in the reaction of these carboranylphosphanes with I(2) in EtOH. Whereas the formation of P four-coordinated molecular "spoke" charge-transfer complexes, (carboranyl)(i)Pr2P-I-I, are suggested for (carboranyl)(i)Pr2P in low polarity solvents, ionic species are formed in ethanolic solutions, which deboronate in a few days, faster than (carboranyl)Et2P, to yield the zwitterionic species. This is attributed to the higher basicity of (carboranyl)(i)Pr2P vs. (carboranyl)Et2P. The X-ray crystal structure of [7-PI(i)Pr2-8-Ph-7,8-nido-C2B9H10], 2c, obtained from the reaction of 1-P(i)Pr2-2-Ph-closo-1,2-closo-C2B10H10 with I(2) in EtOH, confirms the formation of the zwitterion. These results prove that minor changes in the nature of the R substituents on the P atom in carboranylphosphanes, along with the solvent in which the reaction takes place, produce major alterations in the geometry of the (carboranyl)R2P-I-I species in solution, and in their possible further reactivity.     

2‐Methyl‐1‐phenylsulfanyl‐1,2‐dicarba‐closo‐dodecaborane(12)

In the title o‐carborane derivative, C₉H₁₈B₁₀S, the methyl and phenyl­sulfanyl groups are connected to the C atoms of the carborane cage. The C_cage—C_cage distance is 1.708 (4) Å.     

Restricted rotation in unbridged sandwich complexes: rotational behavior of closo-[Co(eta 5-NC4H4)(C2B9H11)] derivatives

Rotation about the centroid/metal/centroid axis in ferrocene is facile; the activation energy is 1-5 kcal mol(-1). The structurally similar sandwich complexes derived from closo-[3-Co(eta5-NC4H4)-1,2-C2B9H11] (1) have a different rotational habit. In 1, the cis rotamer in which the pyrrolyl nitrogen atom bisects the carboranyl cluster atoms is 3.5 kcal mol(-1) more stable in energy than the rotamer that is second lowest in energy. This cis rotamer is wide, spanning 216 degrees , and may be split into three rotamers of almost equal energy by substituting the N and the carboranyl carbon atoms adequately. To support this statement, closo-[3-Co(eta5-NC4H4)-1,2-(CH3)2-1,2-C2B9H9] (2), closo-[3-Co(eta5-NC4H4)-1,2-(mu-CH2)3-1,2-C2B9H9] 3, 2-->BF3, and 3-->BF3 have been prepared. Two rotamers are found at low temperature for 2-->BF(3) and 3-->BF3. Compounds 2, 3, and 1-->BF3 behave similarly to 1. Rotational energy barriers and the relative populations of the different energy states are calculated from 1H DNMR spectroscopy (DNMR, dynamic NMR). These results agree with those of semiempirical calculations. Without exception, the cis rotamer is energetically the more stable. The fixed conformation of 1 assists in elucidating the rotational preferences of the [3,3'-Co(1,2-C2B9H11)2]- ion in the absence of steric hindrance; the [3,3'-Co(1,2-C2B9H11)2]- ion is commonly accepted to present a cisoid orientation. Complex 1 is electronically similar to the [3,3'-Co(1,2-C2B9H11)2]- ion. Both have heteroatoms in the pi ligands, and they have the same electronegativity difference between the constituent atoms. This leads to a view of the [NC4H4]- as [7,8-C2B9H11]2- ion, with no steric implications. Therefore the [3,3'-Co(1,2-C2B9H11)2]- ion should be considered to have a cisoid structure, and the different rotamers observed to be the result of steric factors and of the interaction of the counterion with either B-H groups and/or ancillary ligands. The rotamer adopted is the one with the atoms holding the negative charges furthest apart.