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The hydrides HRh(depe)2and HRh(dmpe)2(depe Et2PCH2CH2PEt2, dmpe Me2PCH2CH2PMe2) have thermodynamic hydride donor abilities comparable to LiHBEt3, as indicated by their ability to transfer a hydride ligand to Et3B to sequentially form Et3BHBEt3-and HBEt3-. HRh(depe)2and HRh(dmpe)2can be generated from Rh(dmpe)2(CF3SO3) and Rh(depe)2(CF3SO3) and hydrogen gas in the presence of a strong base such as potassium tert-butoxide or lithium diisopropylamide. This reaction proceeds through the oxidative addition of hydrogen to form the H2Rh(diphosphine)2(CF3SO3) complexes, followed by deprotonation. The oxidative addition of H2is favored by diphosphine ligands with electron-donating substituents and large chelate bites. In the present study, the driving force for oxidative addition of H2follows the order Rh(dmpe)2(CF3SO3) > Rh(depe)2(CF3SO3) > Rh(dppe)2(CF3SO3) with Rh(dmpe)2(CF3SO3) binding H2more strongly than Rh(dppe)2(CF3SO3) (dppe Ph2PCH2CH2PPh2) by at least 2.7 kcal/mol. The effect of the chelate bite size is larger. H2Rh(depx)2(CF3SO3) (depx 1,2-(Et2PCH2)2C6H4) binds H2more strongly than Rh(depe)2(CF3SO3) by 12 kcal/mol. An understanding of both hydrogen activation and hydride donor abilities is important for developing powerful hydride donors from H2.

The syntheses and characterizations of Cp‘ ‘ReCl2(SC3H6S), 1, Cp‘ ‘ReCl3(SCHMe2), 2, and Cp‘ ‘ReCl2(SCHMe2)2, 3, are reported (Cp‘ ‘ = C5Me4Et). Complex 2 has been characterized by an X-ray diffraction study, which confirms its mononuclear structure. Reactions of 1, 2, and 3 have been studied and compared with those characterized previously for Cp‘ ‘ReCl2(SC2H4S). For example, the thermal reaction of 1 in toluene at 100 °C, results in the elimination of HCl and formation of a complex with a chelated thiolate/thialdehyde ligand, Cp‘ ‘ReCl(SCH2CH2CH&dbd;S), 5. Complex 5 can also be synthesized at a lower temperature by the reaction of 1 with excess triethylamine. Spectroscopic characteristics and reactivity of 5 are reported.

The complexes (1-Me-Ind)(PR3)Ni−Cl (Ind = indenyl; R = Me (2), Cy (3), Bu (4), and (CH2)2(CF2)5CF3 (5)) have been prepared by the direct reaction of the corresponding (PR3)2NiCl2 with Li(1-Me-Ind) or via phosphine exchange reactions with (1-Me-Ind)(PR‘3)Ni−Cl (R‘ = Ph (1) and Me). Solution NMR and single-crystal X-ray diffraction studies of the structures of 2 and 3 have allowed an analysis of the mode of coordination of the 1-Me-Ind ligand both in the solid state and in solution. Kinetic studies have shown that the substitution of PPh3 in (1-Me-Ind)(PPh3)Ni−Cl by PCy3 follows a second-order rate (associative mechanism) with the following kinetic parameters:  K2 (× 10^-2 M^-1 s^-1) = 1.1 ± 0.1 at 233 K, 1.9 ± 0.4 at 245 K, 15 ± 2 at 284 K, 21 ± 2 at 293 K, and 34 ± 7 at 303 K; ΔH^&thermod; = 6.40 ± 0.07 kcal/mol; ΔS^&thermod; = −40 ± 4 eu. The implications of these results for the mechanisms of the polymerization reactions catalyzed by these complexes have been discussed.

A linear free-energy relationship exists between the half-wave potentials of the (II/I) couples of Ni(diphosphine)2 complexes and the hydride donor ability (ΔG°H^{−) of the corresponding [HNi(diphosphine)2]+ complexes. A similar correlation is observed between the half-wave potentials of the (I/0) couples of Ni(diphosphine)2 complexes and the pKa values (or ΔG°H+) of the corresponding [HNi(diphosphine)2]+ complexes. As a result, it is possible to use the potentials of these two couples to predict the free energies of all three Ni−H bond cleavage reactions, ΔG°H+, ΔG°H•, and ΔG°H−, for this class of nickel complexes. The molecular structures of Ni(Et2PCH2CH2PPh2)2 and Ni(Ph2PCHCHPPh2)2 were determined by single-crystal X-ray diffraction studies.}

The nickel indenyl compounds Ind(PR3)Ni-X (Ind = indenyl and its substituted derivatives; R = Ph, Cy, Me; X = Cl, Me, CCPh) can dimerize and/or polymerize ethylene in the presence of suitable activators. For example, poly(methylaluminoxanes) (PMAO) combine with these Ni precursors to produce catalytically active species for both the dimerization and polymerization of ethylene. The polymers obtained from these reactions are mostly linear polyethylenes which contain a small number of ethyl branches and exhibit molecular weights in the range of Mw = 10⁵ (Mw/Mn ca. 2). On the other hand, using activators such as AgBF4, AlCl3, and B(C6F5)3 leads to the exclusive formation of butenes. It is proposed that the latter activators convert the Ni precursors to the highly electrophilic cations [IndNi(PR3)]⁺, which efficiently catalyze the dimerization of ethylene to butenes; in contrast, Ni/PMAO combinations give both the aforementioned cationic species as well as neutral species bearing a Ni(μ-Me)Al core, which is thought to be the active site for the polymerization reactions.

The electrophilic tetranuclear complex [(Cp‘Mo(μ-S))2(S2CH2)]2(BF4)2 (1:  Cp‘ = C5H5 (1a), C5H4Me (1b)), in which two dinuclear complexes are joined by a sulfur−sulfur bond, reacts with the electron-rich nitrogen heterocycles pyrroles and indoles at room temperature. The reactions involve heterolytic scission of the disulfide bond by the nucleophiles followed by proton transfer, and the products are [(Cp‘Mo)2(S2CH2)(μ-S)(μ-SH)]BF4 (2) and [(Cp‘MoS)2(S2CH2)(μ-S)(μ-S-pyrrolyl)]BF4 (3−6). The reactions have been characterized for pyrrole, 1-methylpyrrole, 1,2,5-trimethylpyrrole, and 1-methylindole. The regiochemistry of the reactions depends on pyrrole substituents. Complex 1 also reacts readily with the coordinated pyrrolyl ligand in (PMe2Ph)3Cl2Re(NC4H4). The electrophilic substitution occurs on the 3-position of the heterocycle to form [(Cp‘Mo)2(S2CH2)(μ-S)(μ-SC4H3N)ReCl2(PMe2Ph)3]BF4 (7). Complex 7 undergoes a further reaction with 1 to give the hydrogen abstraction product [(Cp‘Mo)2(S2CH2)(μ-S2C4H2N)ReCl2(PMe2Ph)3]BF4 (8). An X-ray diffraction study of 8b confirms that the 3- and 4-carbons of the pyrrolyl ligand are coordinated to the μ-sulfido ligands of the molybdenum dimer. The new products suggest that there are a number of ways in which electron-rich heterocycles might interact with a sulfided molybdenum catalyst in the hydrodenitrogenation reactions. Reactions of 1 with other nucleophiles have also been surveyed.

Four [5.5](2,6)pyridinophanes and -cyclophanes containing silylene units (2a,b, 3a,b) have been prepared by reacting dichlorosilanes with pyridine- or benzenedimethanol. X-ray structures of compounds 2a, 2b, and 3a have been determined. The diphenylsilylene pyridinophane 2b and dimethylsilylene cyclophane 3a were found to adopt an anti conformation in the solid state. In contrast, the dimethylsilylene pyridinophane 2a exhibits a syn arrangement. The conformational preference of these cyclophanes without the influence of the packing energy was analyzed by molecular mechanics calculations. The results show that all the derivatives preferentially adopt a syn conformation, whereas the anti geometry found in the solid state for 2b and 3a does not play a significant role in the conformational equilibrium at room temperature.

The reaction of RuCl2(PPh3)3 with pyrrolyllithium results in the formation of the pyrrolyl complex (NC4H4)RuCl(PPh3)2, 1, which has been characterized by an X-ray diffraction study. The structure confirms the η⁵-bonding mode for the pyrrolyl ligand. Ligand substitution reactions with 1 have led to the facile synthesis of related η⁵-pyrrolyl ruthenium complexes with other suppporting ligands. Reactions of the PEt3 derivatives (NC4H4)RuX(PEt3)2, X = Cl and I, with aryl- and alkyllithium reagents resulted in nucleophilic substitution of the pyrrolyl ligand accompanied by hydrogen transfer to the metal ion, forming (2-RNC4H3)RuH(PEt3)2. The hydride products could be converted to the corresponding chloride derivatives in chlorinated solvents, and the complex (2-PhNC4H3)RuCl(PEt3)2 has been structurally characterized. A second nucleophilic substitution reaction on the coordinated pyrrolyl ligand has been characterized in some cases, and protonation of the substituted pyrrole complex led to isolation of the free substituted pyrrole with recycling of the ruthenium complex. The nucleophilic substitutions are sensitive to the electronic features of the supporting ligands in the complex and to the strength of the nucleophiles.