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The geometries and energies of mononuclear and binuclear octafluorocyclohexadiene iron carbonyl derivatives have been studied using density functional theory. The lowest energy C6F8Fe(CO)3 tricarbo...

Lithiation of an imidazole-based monothiolate, 2, by excess n-butyllithium gives a white powder containing both a lithiated product and an nBuLi contaminant (in a ca. 1:1 molar ratio). This white p...

Lithium-containing molecules, such as C2H2Li2, C6Li6, and several lithium halides, have been studied in the present paper, and the nature of lithium bonds in these structures is investigated. In co...

A series of imidazolium-based synthetic routes to imidazolium cyclopentadienides are reported. The 2:1 reaction of imidazolium (1) with [Cp2TiIIICl]2 gives [NHCDippH]+[Cp2TiIIICl2]− (NHCDipp = 2,6-diisopropylphenyl-substituted N-heterocyclic carbene) (2). The “inverse sandwich” imidazolium cyclopentadienide (3) is obtained as a crystalline solid via reaction of 1 with both [Cp2TiIIICl]2 and cyclopentadienyllithium (CpLi) (in a molar ratio of 2:1:1) in THF/toluene at elevated temperature. Notably, the 1:1 reaction of 1 with CpLi leads to the isolation of “multidecker” 4 in the solid state, while the corresponding 1:2 reaction of 1 with CpLi gives the crystals of CpLi-bound cyclopentadienyl-imidazolium complex 5. While compounds 3, 4, and 5 have been structurally characterized using single-crystal X-ray diffraction, in solution these complexes dissociate due to the conversion of [NHCDippH]+[Cp]− to both cyclopentadiene and NHCDipp through intramolecular proton transfer. The equilibrium of the acid–base conv...

MnBr(N-ethyl-N′-2-pyridylimidazol-2-ylidine)(CO)3 reduces CO2 to CO in the absence of strong acids. Herein, we employ density functional theory and domain based local pair natural orbital coupled cluster theory to perform the first mapping of the catalytic pathway for this catalyst and various derivatives. The benzimidazole-containing derivative proceeds along the same pathway as its parent complex, but with an increased barrier to H+ reduction. The phenolated complex shows barrierless CO2 addition to the activated catalyst and facile C–O bond cleavage. All species exhibit a novel pyridine dissociation upon one-electron reduction of the tetracarbonyl species, but the active tricarbonyl catalysts can be regenerated with a small barrier. This novel step in the pathway presents a further consideration in the design of catalysts and provides insight into the potential degradation pathways of this catalyst.

The synthesis and characterization of new Mn(I)- and Re(I)-centered organometallic complexes fashioned with 1,4-diazabutadiene (DAB) ligands is reported. Ten compounds of the type fac-(α-diimine)M(CO)3Br (M = Mn, Re) were obtained in moderate to excellent yield (35–80%) and high purity from the coordination of the five ligands with M(CO)5Br in refluxing ethanol. Despite the electronic similarity of DAB to 2,2′-bipyridyl, the complexes described herein were poor mediators of electrochemical CO2 conversion to CO, but provide insight into the role of redox-active ligands in catalysis. Additional characterization of the one-electron reduced rhenium compounds, relevant intermediates in CO2 reduction, by EPR and single-crystal X-ray analysis is described.

The relative energies of singlet and triplet metallocene, metallabenzene, and metallacyclopentadiene C10H10M isomers (M = Ni, Pd, Pt) have been examined using density functional theory. For the C10H10Ni system, the experimentally known triplet nickelocene (η5-Cp)2Ni is the lowest energy isomer by ∼17 kcal/mol with respect to singlet nickelocene. For the C10H10Pd system, the triplet and singlet palladocene structures have similar energies within ∼2 kcal/mol. However, the singlet palladocene has a “slipped ring” (η3-Cp)2Pd structure with two trihapto Cp rings. The C10H10Pt system is different since the platinabenzene CpPtC5H5 isomer is the lowest energy structure. This is in accord with the synthesis of stable substituted CpPtC5H3R2 platinabenzenes by Haley and co-workers [Haley, M. M.; et al. Organometallics 2004, 23, 1174]. However, the slipped ring singlet platinocene (η3-Cp)2Pt to the isomeric platinocene lies only ∼2 kcal/mol above the platinabenzene global minimum, so the energy barrier for conversion...

Buchalski and co-workers showed in 2008 that reactions of the nickelafluorenyl anion CpNiC12H8– with MX2 (M = Co, Ni) give the dinickelametallocene sandwich compounds (CpNiC12H8)2M. We now report theoretical studies on the related bis(nickelacyclopentadienyl)metal derivatives (CpNiC4H4)2M and bis(nickelaindenyl)metal derivatives (CpNiC8H6)2M as well as the bis(nickelafluorenyl)metal derivatives. The structures of the lowest energy bis(nickelacyclopentadienyl) sandwich compounds (CpNiC4H4)2M may be derived from those of the corresponding metallocenes Cp2M by replacing a CH group in each Cp ring with an isolobal CpNi unit. The Ni–M distances of ∼2.5 A indicate formal single bonds and thus a pentahapto η5-CpNiC4H4 ligand. The spin states of the lowest energy (CpNiC4H4)2M derivatives are similar to those of the corresponding metallocenes Cp2M, namely, singlet, doublet, and triplet for M = Fe, Co, and Ni, respectively. Fusion of benzene rings to the nickelacyclopentadienyl rings to give first the bis(nickelain...

The tetramethyleneethane (TME) ligand is found in the η3,η3 complex trans-(η3,η3-TME)Ni2Cp2 and the η4,η4 complex trans-(η4,η4-TME)Co2Cp2, which have both been synthesized and structurally characterized by X-ray crystallography. The structures of the complete series of (TME)M2Cp2 derivatives of the first-row transition metals from Ti to Ni have now been investigated by density functional theory. The experimentally known nickel and cobalt complexes are found to have closed-shell electronic ground states. The lowest energy structure for the iron complex is the triplet spin state trans-(η4,η4-TME)Fe2Cp2 structure with geometry similar to that of the lowest energy cobalt structure. All of the low-energy (TME)M2Cp2 structures for manganese and the first-row transition metals to the left of manganese (Cr, V, and Ti) exhibit cis-(η4,η4-TME)M2Cp2 stereochemistry, thereby providing the possibility for direct metal–metal interactions. Vanadium is the only first-row transition metal to the left of cobalt where the l...

The so-called flyover complexes (η3,1,η3,1-μ-R3R′3C6)Co2(CO)4 are important because of their role as intermediates in the cobalt carbonyl-catalyzed cyclotrimerization of alkynes. A density functional study of such flyover complexes has led to the discovery of isomers with bent benzene rings bridging a pair of cobalt atoms. Such complexes are likely to be involved in the process of forming a carbon–carbon bond in closing the six-carbon chain in the flyover complexes to give the corresponding arene derivatives. The relative energies of the flyover complexes and the bridging bent benzene derivatives depend on the substituents on the six-carbon chain. Thus, for [C6(CF3)6]Co2(CO)4 and [1,3,6-tBu3C6H3]Co2(CO)4 with bulky CF3 and tert-butyl substituents at the ends of the six-carbon chain, the experimentally known flyover complexes are preferred energetically over the isomeric bridging bent benzene ring structure by 23.3 and 1.1 kcal/mol, respectively. However, for the less sterically hindered (C6R6)Co2(CO)4 (R ...

Complexation of the very unstable free heptafulvene with iron carbonyls is known experimentally to lead to stable complexes, including two isomers of (η4-C7H6CH2)Fe(CO)3 as well as the binuclear (C7H6CH2)2Fe2(CO)6. Density functional theory shows that structures of the mononuclear (C7H6CH2)Fe(CO)3 with trimethylenemethane and butadiene subunits of the heptafulvene ligand bonded to the Fe(CO)3 moiety have nearly equal energies within ∼3 kcal/mol, consistent with the experimental observation of two isomers depending upon the synthetic method. For (C7H6CH2)Fe2(CO)6 a trans-η4:η4 structure with no iron–iron bond and a cis-η3:η3 allylic structure with an iron–iron bond are predicted to have energies within ∼3.0 kcal/mol. Comparison of the predicted ν(CO) frequencies for these two structures with the experimental ν(CO) frequencies for the structurally uncharacterized (C7H6CH2)Fe2(CO)6 suggests the cis-η3:η3 allylic structure for the latter.

The recent (2011) discovery of two nine-electron donor bridging indenyl ligands in the cobalt sandwich complex {η5,η4-Me3Si)2C9H5}2Co2 makes of interest a search for structures of metal carbonyl derivatives with such indenyl ligands. In this connection, density functional theory studies on the binuclear iron carbonyls (C9H7)2Fe2(CO)n (n = 4, 3) predict structures having terminal pentahapto indenyl ligands similar to the experimentally known structures for their cyclopentadienyl analogues (C5H5)2Fe2(CO)n. Thus, the lowest-energy (C9H7)2Fe2(CO)4 structures are singlets with two bridging CO groups. Similarly, the lowest-energy (C9H7)2Fe2(CO)3 structures are triplets with three bridging CO groups and terminal pentahapto indenyl ligands. However, a nine-electron donor bridging indenyl ligand is found in the lowest-energy (C9H7)2Fe2(CO)2 structure, which has an Fe–Fe single bond and two terminal CO groups. Higher-energy (C9H7)2Fe2(CO)2 structures with terminal pentahapto indenyl ligands and short (∼2.1 A) Fe≡Fe...

Reaction of Fe2(CO)9 with 3-chloro-2-(chloromethyl)propene is known to give the stable iron tricarbonyl complex [η4-(CH2)3C]Fe(CO)3, containing the umbrella-shaped trimethylenemethane ligand. The mononuclear complexes (CH2)3CFe(CO)n (n = 1–4) and the binuclear complexes [(CH2)3C]2Fe2(CO)n (n = 3–5) of this trimethylenemethane ligand have been studied here. The lowest energy [(CH2)3C]2Fe2(CO)5 structure has one bridging CO group and an Fe–Fe single bond but is disfavored with respect to dissociation into the mononuclear fragments [(CH2)3C]2Fe2(CO)3 + [(CH2)3C]2Fe2(CO)2. The lowest energy [(CH2)3C]2Fe2(CO)4 structure has two semibridging CO groups and an Fe═Fe double bond but is disfavored with respect to disproportionation into [(CH2)3C]2Fe2(CO)5 + [(CH2)3C]2Fe2(CO)3. In contrast to [(CH2)3C]2Fe2(CO)5 and [(CH2)3C]2Fe2(CO)4, the tricarbonyl [(CH2)3C]2Fe2(CO)3 appears to be a reasonable synthetic objective. The lowest energy structure has one terminal CO group, one semibridging CO group, one symmetrical bri...

The lowest energy Cp2Fe2(BF)2(CO) structure is predicted by theory to have an iron–iron bond bridged by both a difluorodiborene ligand and a carbonyl group. Such a structure is potentially accessible by reaction of B2F4·OEt2 with the highly nucleophilic NaFe(CO)2Cp followed by decarbonylation.

A series of dinuclear alkaline earth metal (Ae) structures Na2[(CHNH)2Ae–Ae(CHNH)2] (1–5) and (CHNH)2Ae–Ae(CHNH)2 (6–10) containing Ae–Ae bonds were optimized using density functional theory (DFT) and hybrid Hatree-Fock/DFT methods. The geometric and NBO analyses indicate that there are covalent Ae–Ae bonds in these α-diimine-stabilized structures, which have been further investigated by NBO second-order interaction and bond dissociation energetic examinations.

The first anionic N-heterocyclic dicarbene−borane binuclear complexes, Li+·[H3B:C{[N(2,6-Pri2C6H3)]2CHC:BH3}]− (V) and Li+(THF)3·[H3B:C{[N(2,6-Pri2C6H3)]2CHC:BEt3}]− (VI), were synthesized by combining BH3·THF with [:C{[N(2,6-Pri2C6H3)]2CHCLi}]n (III) and (THF)2Li:C{[N(2,6-Pri2C6H3)]2CHC(BEt3)} (IV), respectively. X-ray crystal structures of a (V·THF)n polymer, a V·(DME)2 monomer, a (V·DME)2 dimer, and a VI monomer were obtained. The nature of the bonding of V and VI was probed further by computations.

Saouma, Muller, and Peters recently (J. Am. Chem. Soc., 2009) reported the synthesis of several diiron complexes with two types of bridging diazene HN═NH ligands, designated μ-η1:η1 (bridging end-on) and μ-η2:η2 (bridging side-on), with tridentate phosphine {XBPR3} ligands ({XBPR3} = XB(CH2PR2)3−; X = Ph; R = Ph, CH2Cy). In the present study the energies, optimized geometries, and vibrational frequencies of these complexes with X = H and R = H, CH3, CF3 were obtained theoretically, and the electronic structures were analyzed in terms of iron−diazene donor−acceptor interactions. Natural bond orbital analysis indicates that both bridging end-on and side-on diazenes possess strong π-acceptor properties, which cause significant occupation of their antibonding π*(N−N) LUMOs and weakening of the N−N bonds as the result of coordination. The most pronounced weakening was obtained in complexes with bridging side-on diazene, where interaction of iron d-AOs with π*(N−N) orbitals of the diazene ligands results in the...

Comparison of the lowest energy Cp2Nb2(CO)n structures (n = 7, 6, 5, 4, 3, 2, 1) with the corresponding Cp2V2(CO)n structures using density functional theory predicts structures having four-electro...

The (acetylene)dicobalt carbonyl complexes H2C2Co2(CO)n (n = 6−4) have been studied using density functional theory. The preferred structure for H2C2Co2(CO)6 is predicted to be an eclipsed structur...

The binuclear cyclopentadienylosmium carbonyls Cp2Os2(CO)n (Cp = η5-C5H5; n = 4, 3, 2) have been studied by density functional theory (DFT). The unbridged Cp2Os2(CO)4 structure found experimentally is predicted to be of lower energy than the doubly bridged structures cis- and trans-Cp2Os2(CO)2(μ-CO)2, in contrast to the analogous iron system. However, the energy differences are rather small (∼5 kcal/mol). The Cp2Os2(CO)3 system differs from its iron analogue in that the triplet structure Cp2Os2(μ-CO)3 analogous to the known, stable Cp2Fe2(μ-CO)3 lies at least ∼12 kcal/mol above the lowest energy singlet structure. Thus the three lowest lying Cp2Os2(CO)3 structures are all singlet structures, which are either unbridged or doubly bridged. The iron and osmium dicarbonyl systems Cp2M2(CO)2 (M = Fe, Ru) are analogous in that the lowest energy structures are doubly bridged with short M≡M distances suggesting the formal triple bonds required to give both metal atoms the favored 18-electron configuration. The pro...

A Zn−Zn-bonded compound, [K(THF)2]2[(LiPr)Zn−Zn(LiPr)] (2) and three mononuclear zinc compounds, [Zn(LMe)2Na2(Et2O)2] (3), [Zn(LEt)2Na2(THF)2] (4), and [Zn(LEt)2K2]n (5), with N-aryl substituted α-diimine ligands LiPr, LMe, and LEt (L = [(2,6-R2C6H3)N(Me)C]2, R = iPr, Me, Et, respectively) have been synthesized from the reduction of the LZnCl2 precursors by the alkali metal Na or K. X-ray structural analyses show that the compounds have a [Zn2L2]2− (2) or [ZnL2]2− (3−5) core incorporating Na+ or K+ ions solvated by THF or Et2O molecules, except for 5, which displays a 2D polymeric structure formed by intermolecular K−C bonds due to the lack of K−solvent interactions. In compound 2, the formal Zn2+ ion in the precursor is reduced to Zn+, while in 3−5 it remains unreduced. The neutral ligands in the precursor, however, are doubly reduced to a dianion, L2−, in all compounds, as evidenced by the bond lengths of the N–C═C–N moiety of the ligands. Effects of the ligand substituent, reducing agent, and solvent o...

A series of sodium and magnesium complexes with α-diimine ligands, [Na2(LiPr)(Et2O)]2 (1, LiPr = [(2,6-iPr2C6H3)N(Me)C]2), [Na2(LMes)(solv)2]2 (LMes = [(2,4,6-Me3C6H3)N(Me)C]2, 2a, solv = Et2O; 2b, solv = THF), [Na4(LEt)2]n (3, LEt = [(2,6-Et2C6H3)N(Me)C]2), and [Mg(LMes)(THF)3] (4), have been synthesized by reduction of the diimine ligands with sodium or magnesium metal. Single-crystal X-ray diffraction analysis revealed that the sodium complexes have a 2:1 [Na2L] unit that aggregates to dimeric (1, 2a, 2b) or polymeric (3) structures, while the magnesium complex (4) shows a monomeric 1:1 structure. In all compounds 1−4, the ligand is doubly reduced to a dianion. The two Na+ ions in 1, 2a, 2b, and 3 show different coordination modes, one of which is chelated by the N donors of a ligand with supplementary Na−C bonds to the phenyl ring of another ligand within the [Na2L]2 dimer, while the other is bonded by the central C2N2 core of the ligand and solvent molecules (1, 2a, and 2b). Compound 3 displays a nov...

The rates of reaction of N2CHSiMe3 with HMo(CO)3Cp (Cp = η5-C5H5) in heptane obey the rate law −d[HMo(CO)3Cp]/dt = k[HMo(CO)3Cp][N2CHSiMe3] (k = 0.035 ± 0.01 M−1 s−1 at 0 °C; ΔH⧧ = 11.7 ± 2.0 kcal/mol and ΔS⧧ = −22.0 ± 3.0 cal/(mol K)). Isotopic scrambling between DMo(CO)3Cp and N2CHSiMe3 occurs at a rate faster than the overall reaction. Reversible 1,2-addition to form the tightly bound intermediate [Me3SiCH2Nβ═Nαδ+][δ−Mo(CO)3Cp] is proposed as the first step of the reaction. Spectroscopic and computational data support this formulation. The contact ion pairs can undergo heterolytic cleavage to ions or homolytic cleavage to radicals, and the solvent influence on kobs (THF > toluene > heptane) is interpreted in terms of this model. The enthalpy of this reaction has been measured by solution calorimetry at 272 K in THF: ΔH = −11.6 ± 1.2 kcal/mol. These data, together with computed organic reaction energies allow estimation of the bond strength between the three-electron donors·N2CHSiMe3 and ·Mo(CO)2Cp to b...

The binuclear benzenemanganese carbonyls (η6-C6H6)2Mn2(CO)n (n = 4, 3, 2, 1) have been studied by density functional theory (DFT) using the B3LYP and BP86 methods. The singlet doubly bridged and unbridged isomers of the saturated (η6-C6H6)2Mn2(CO)4 are nearly degenerate, suggesting a highly fluxional system. The global minimum of (η6-C6H6)2Mn2(CO)3 is a triplet electronic state—a triply bridged isomer analogous to the known isoelectronic triplet Cp2Fe2(μ-CO)3. The doubly bridged singlet structure (η6-C6H6)2Mn2(CO)(μ-CO)2 lies 9 kcal/mol (B3LYP) or 7 kcal/mol (BP86) above this global minimum. The global minimum of (η6-C6H6)2Mn2(CO)2 is a doubly bridged structure with a short manganese−manganese distance suggestive of a Mn≡Mn triple bond. Singlet and triplet structures are found for (η6-C6H6)2Mn2(CO) with a two-electron donor CO group and metal−metal distances suggesting a M−M quadruple bond for the singlet state and a M≡M triple bond for the triplet state.

In view of experimental work on (η4-C4H4)2Fe2(μ-CO)3 the full range of binuclear cyclobutadieneiron carbonyls (η4-C4H4)2Fe2(CO)n (n = 5, 4, 3, 2, 1) have been studied by density functional theory using the B3LYP and BP86 functionals. The pentacarbonyl (η4-C4H4)2Fe2(CO)5 is predicted to have a singly bridged (η4-C4H4)2Fe2(CO)4(μ-CO) structure with an Fe−Fe single-bond distance of 2.743 A (BP86). For (η4-C4H4)2Fe2(CO)4 cis and trans doubly CO-bridged singlet structures are found as well as two types of doubly CO-bridged triplet structures. One type has Fe−Fe bond distances in the single-bond range 2.64−2.66 A and 17-electron iron configurations. The other type of triplet structure has Fe═Fe bond distances in the range 2.38−2.39 A for a σ + 2/2π double bond like that in dioxygen and 18-electron iron configurations. For (η4-C4H4)2Fe2(CO)3 the global minimum is the experimentally observed triply CO-bridged structure with an Fe≡Fe distance of 2.148 A (BP86), corresponding to the triple bond required for 18-elec...

The binuclear (cyclobutadiene)cobalt carbonyls (η4-C4H4)2Co2(CO)n (n = 1−4) have been studied by density functional theory (DFT) using the B3LYP and BP86 methods. The singlet doubly bridged and unb...

The synthesis and characterization of new Mn(I)- and Re(I)-centered organometallic complexes fashioned with 1,4-diazabutadiene (DAB) ligands is reported. Ten compounds of the type fac-(α-diimine)M(CO)3Br (M = Mn, Re) were obtained in moderate to excellent yield (35–80%) and high purity from the coordination of the five ligands with M(CO)5Br in refluxing ethanol. Despite the electronic similarity of DAB to 2,2′-bipyridyl, the complexes described herein were poor mediators of electrochemical CO2 conversion to CO, but provide insight into the role of redox-active ligands in catalysis. Additional characterization of the one-electron reduced rhenium compounds, relevant intermediates in CO2 reduction, by EPR and single-crystal X-ray analysis is described.

Twenty-four group 13−group 16 chalcogen heterocubanes [RM(μ3-E)]4 (R = H, CH3; M = Al, Ga, In; E = O, S, Se, Te) and 12 group 13−group 13 pure cubanes [RM(μ3-M)]4 (R = F, Cl, CH3, NO2; M = Al, Ga, In) have been studied using density functional theory. Geometries and thermodynamic properties were computed at the B3LYP/SRLC level. All structures were found to be true minima with at most 0.08 A and 2.5° deviation from the limited experimental geometries. These chalcogen heterocubanes appear thermodynamically resistant to fragmentation. The M4E4 core for each structure proved to be insensitive to ligand choice for the group 13−group 16 heterocubanes. By contrast, the electron-deficient M8 cores of the pure cubanes were variously affected by the electronegativity of various R groups. The entropically disfavored nature of the synthesis may hold the key to the as-yet-unsynthesized [RAl(μ3-O)]4.

Potential energy surfaces for systems consisting of SiH3F and SiH3Cl molecules with addition of two water molecules (as a model for neutral hydrolysis), with one water and one ammonia molecule (base-catalyzed hydrolysis), and with two ammonia molecules (racemization) were investigated by the B3LYP and MP2 methods with 6-31G(d,p) and 6-311+G(d,p) basis sets. It was shown that in addition to global energy minima corresponding to loosely bound complexes with SiO and SiN separations exceeding 2.5 A, there exist the stationary points for tightly bound, low-entropy complexes with SiO and SiN bonds of length ca. 2.0 A. Such complexes were predicted earlier by the analysis of experimental data on nucleophile-assisted hydrolysis and racemization. For SiH3F structures of these complexes are close to octahedral with NH3 or H2O in axial positions, while those for silyl chloride are closer to trigonal bipyramidal zwitterions formed by the SiH3 cation with two nucleophiles and the Cl anion separated from Si by ca. 3 A....

The lithiated N-heterocyclic carbene−phosphinidene adduct L′:P−H (3; L′: = :C{[N(2,6-Pri2C6H3)]2CHCLi(THF)3}) unexpectedly resulted from the reaction of lithium metal with the carbene-stabilized diphosphorus species L:P−P:L (2; L: = :C{N(2,6-Pri2C6H3)CH}2). Compound 2 was previously prepared by the potassium graphite reduction of L:PCl3 (1).

Ab initio and density functional (BHLYP, B3LYP, and BP86) quantum mechanical methods were applied to predict the structures, properties, and stabilities (M = Li, Na, K) three-membered ring systems. These structures derive from the previously theoretically and experimentally characterized parent homonuclear cyclogallenes M2(GaH)3. Basis sets of triple-ζ plus double polarization augmented with diffuse functions (TZ2P+diffuse) quality were employed at self-consistent field (SCF) and density functional levels of theory. Equilibrium geometries, harmonic vibrational frequencies, and chemical shifts are reported to facilitate experimental verification of the computed structures. All title compounds are minima and their geometries as well as their properties compare well with the cyclogallene three-membered ring compounds M2(GaH)3. Singly and even may well be feasible experimental targets. The large negative nucleus independent chemical shifts (NICS), used as a criterion for aromatic cyclic delocalization, sugges...

Main group bis-element sandwiches formed by donor−acceptor interactions of MCp and ECp (M = Li, Na, K; E = B, Al, Ga) have been studied at the B3LYP/pVDZ level of theory. The most stable are boron-containing species which are stabilized by electrostatic interactions, while other compounds are destabilized. The stability of the donor−acceptor bond decreases in the row B > Al > Ga for donors and Li > Na > K for acceptors. The Cp* group enhances donor properties by 10−15 kJ mol-1. We predict that these new compounds are viable synthetic targets.