An investigation of the properties and thermochemistry of complexes of pyridine with triphenyl-boron, -aluminium, -gallium, and -indium, and diphenylgallium chloride

Abstract

The problems attending the estimation of gas-phase heats of formation and the calculation of reorganization energies are discussed and the results compared with those available on other Group I l l acceptors.A considerable body of data has been published on the heats of formation of co-ordination complexes of the halides 1 and aliphatic derivatives of the Group I11 eleinents.2 The corresponding aryl compounds however have been almost completely neglected and no thermochemical data whatsoever exist with regard to complex formation by these systems. It was the purpose of the present work to obtain such information and to compare the acceptor properties of the aryl compounds with those of the halides and alkyl systems. Such a comparison is particularly cogent in the light of recent work3 on the x bonding energies of these systems, a factor which is usually considered to be dominant in determining the strength of an electron acceptor. RESULTS AND DISCUSSIOXGeneral Pro$erties.-All the four triphenyl compounds and diphenylgallium chloride reacted with liquid pyridine at room temperature yielding, finally, stable solid 1 : 1 complexes. Two of these complexes, Ph3B,py and Ph,Al,py, have been reported previously 4,5 but since the recorded melting points were about 30" lower than ours it seems that they were to some extent impure. Triphenylindium initially retained more than 1 mole of yyridine per mole of Ph31n (although the excess was evolved on heating) thus indicating that the 1 : 1 complex is the most stable. All four compounds are essentially monomeric in benzene solution. The lower degree of association of Ph,In,py in more dilute solution (0.91 wt. yo) suggests that some dissociation of the complex is occurring, a not uncommon effect in Group I11 complexes.Although all four compounds melted without apparent decomposition, vacuum sublimation of Ph,Ga,py at 140" led to a solid which melted 4" lower than the original. The i.r. spectra of the. two substances appeared to be identical and hence it is assumed that only

Synthesis and Calorimetric, Spectroscopic, and Structural Characterization of Isocyanide Complexes of Trialkylaluminum and Tri-tert-butylgallium

“…In particular, Eyman and co-workers reported solution calorimetry data on enthalpies of reactions of trimethylaluminum with simple Lewis bases, such as THF, diethyl ether, amines, sulfides, phosphines, and phosphine oxides, − and Pasynkiewicz extended this work to include nitriles . Similar data have been reported for triethylaluminum by Bonitz and Schubert and co-workers and for triphenylaluminum by Greenwood et al More recently, calorimetry has been used by Marks and co-workers to measure enthalpies of methide abstraction from dimethylmetallocenes of titanium and zirconium using E­(C 6 F 5 ) 3 (E = B, Al) . Calorimetric methods for determining organoaluminum concentrations in solution, and process streams have also been patented .…”

Postsynthetic Systematic Electronic Tuning of Organoplatinum Photosensitizers via Secondary Coordination Sphere Interactions

“…One potential concern with this approach is the instability of the borane adducts relative to covalent substituent bonds, which would limit the utility of the strategy described here. Acknowledging that pyridine–borane interactions (Δ H ° f for Ph 3 B·NC 5 H 5 from pyridine and BPh 3 is −17.9 kcal/mol) are considerably weaker than covalent carbon–heteroatom bonds, all of our experiments indicate good stability of the adducts of complex 1 under the experimental conditions. In addition to the titration experiments described in Figures and , we carried out a number of experiments on isolated borane adducts of 1 .…”

“…In addition, in contrast to the cation receptors, which often utilize crown ethers that are size-matched to only certain cations, pyridine receptors should be able to coordinate to virtually any borane Lewis acid (and many others), allowing the design of versatile platforms for studying the effects of Lewis acid additives on the electrochemical and photophysical properties. Finally, pyridine−borane interactions are thermodynamically stable, 43 permitting isolation of the adducts and their further manipulation and processing. For these reasons, we believe that phosphors with strategically placed pyridines would permit careful postsynthetic alteration of both redox potentials and excited-state energies upon interaction with boranes, which could allow for rapid optimization of the properties for a given application.…”

Tripodal P3XFe–N2 Complexes (X = B, Al, Ga): Effect of the Apical Atom on Bonding, Electronic Structure, and Catalytic N2-to-NH3 Conversion

“…Under identical conditions, the analogous reduction event for 3a occurs at the slightly more negative potential of −2.19 V. 14 The scan rate dependence of all three couples is consistent with a diffusion-controlled process. For comparison, the observed trend in the P 3 X Fe−N 2 [0/1−] redox potentials is also in accordance with the theoretically 29,30 and experimentally 31 determined acceptor ability of XPh 3 according to the order X = Al > Ga > B.…”

“…10 Analogous experiments utilizing 5b and 5c yield slightly different results depending on the conditions. In the case of reaction with 10 equiv of HBAr F 4 and 12 equiv of KC 8 , [M(solv) x ][P 3 X Fe−N 2 ] (X = Al, Ga) is the major terminal Fecontaining product, with very little ligand decomposition observed by 31 P{ 1 H} NMR spectroscopy. On the other hand, use of [H 2 NPh 2 ][OTf] and Cp* 2 Co yields a mixture of compounds that includes P 3 X Fe−N 2 (X = Al, Ga) and products of P 3 X Fe decomposition.…”