NMR studies reveal that complexes Ru(CO)(2)(H)(2)L(2) (L = PMe(3), PMe(2)Ph, and AsMe(2)Ph) can have three geometries, ccc, cct-L, and cct-CO, with equilibrium ratios that are highly dependent on the electronic properties of L; the cct-L form is favored, because the sigma-only hydride donor is located trans to CO rather than L. When L = PMe(3), the ccc form is only visible when p-H(2) is used to amplify its spectral features. In contrast, when L = AsMe(2)Ph, the ccc and cct-L forms are present in similar quantities and, hence, must have similar free energies; for this complex, however, the cct-CO isomer is also detectable. These complexes undergo a number of dynamic processes. For L(2) = dppe, an interchange of the hydride positions within the ccc form is shown to be accompanied by synchronized CO exchange and interchange of the two phosphorus atoms. This process is believed to involve the formation of a trigonal bipyramidal transition state containing an eta(2)-H(2) ligand; in view of the fact that k(HH)/k(DD) is 1.04 and the synchronized rotation when L(2) = dppe, this transition state must contain little H-H bonding character. Pathways leading to isomer interconversion are suggested to involve related structures containing eta(2)-H(2) ligands. The inverse kinetic isotope effect, k(HH)/k(DD) = 0.5, observed for the reductive elimination of dihydrogen from Ru(CO)(2)(H)(2)dppe suggests that substantial H-H bond formation occurs before the H(2) is actually released from the complex. Evidence for a substantial steric influence on the entropy of activation explains why Ru(CO)(2)(H)(2)dppe undergoes the most rapid hydride exchange. Our studies also indicate that the species [Ru(CO)(2)L(2)], involved in the addition of H(2) to form Ru(CO)(2)(H)(2)L(2), must have singlet electron configurations.

The photochemical reaction of Ru(CO)(3)(dppe) and Fe(CO)(3)(dppe)(dppe = Ph(2)PCH(2)CH(2)PPh(2)) with parahydrogen has been studied by in situ-photochemistry resulting in NMR spectra of Ru(CO)(2)(dppe)(H)(2) that show significant enhancement of the hydride resonances while normal signals are seen in Fe(CO)(2)(dppe)(H)(2). This effect is associated with a singlet electronic state for the key intermediate Ru(CO)(2)(dppe) while Fe(CO)(2)(dppe) is a triplet. DFT calculations reveal electronic ground states consistent with this picture. The fluxionality of Ru(CO)(2)(dppe)(H)(2) and Fe(CO)(2)(dppe)(H)(2) has been examined by NMR spectroscopy and rationalised by theoretical methods which show that two pathways for ligand exchange exist. In the first, the phosphorus and carbonyl centres interchange positions while the two hydride ligands are unaffected. A second pathway involving interchange of all three ligand sets was found at slightly higher energy. The H-H distances in the transition states are consistent with metal-bonded dihydrogen ligands. However, no local minimum (intermediate) was found along the rearrangement pathways.

F Overhauser, and related 2-D NMR studies on several salts of the dications [Pd(H 2 O) 2 (BINAP)] 2+ , [Pd(µ-OH)(BINAP)] 2 2+ , and [Pd 2 (µ-OH)(µ-NH(p-RC 6 H 4 ))(BINAP) 2 ], R ) Cl, CH 3 , MeO, and, in one case, [Pd(µ-O 2 PF 2 )(BINAP)] 2 (PF 6 ) 2 , are reported. These solution NMR results, together with DFT calculations, reflect on how the anion interacts with the cation, as well as the extent, and the solvent dependence of the ion pairing. The solid-state structure of [Pd 2 (µ-OH)(µ-{NH(p-Tol)})-(BINAP) 2 ](CF 3 SO 3 ) 2 has been determined.

The synthesis, characterization, and PGSE ((1)H and (19)F) NMR diffusion studies on the cationic [(eta(6)-arene)Mn(CO)(3)][X] (arene = anisole, 4-chloroanisole, and 1,3,5-trimethoxybenzene; X = BPh(4) and BArF) are reported. The tetraphenyl borate complexes of anisole and 4-chloroanisole show surprisingly strong ion pairing in dichloromethane solution, whereas the BArF salts do not. (1)H,(1)H-NOESY data support this anion selectivity. In chloroform solution one finds the usual strong ion pairing for both anions. The solid-state structure of [(eta(6)-1,3,5-trimethoxybenzene)Mn(CO)(3)][BPh(4)] has been determined. (13)C NMR and IR data for the new complexes are reported. The observed IR frequencies are higher for the BArF complexes than for the BPh(4) complexes.

Allylic alcohols, rather than halides, acetates, or carbonates can be used directly in the FriedelCrafts-type coupling with various phenols. The use of a Ru IV , rather than a Ru II , precursor promotes the formation of one H + per cycle so that a large excess of acid is never present in the reaction mixture. Consequently, the leaving group in the oxidative addition reaction is H 2 O, thereby avoiding the production of an unnecessary by-product.An increasing variety of metal-mediated catalytic transformations involving allyl compounds have been developed, and these tools are rapidly becoming indispensable in organic synthesis [1 -5]. Generally, p-or s-allyl species are regarded as important intermediates in these various transformations [6] [7]. Typically, allyl sources such as halides, acetates, or carbonates have been employed since the allyl moiety often requires a leaving group to be effective; however, the direct activation of an allyl alcohol is both economically and environmentally more desirable, in that the leaving group is not wasted.One finds only a modest number of reports in which an allyl alcohol is employed as substrate [8 -13], and Akita and co-workers [8] have summarized several mechanistic possibilities for the use of an alcohol, e.g., either an oxidative addition reaction or a dehydration pathway. The former is not favored because the OH group is thought to be a poor leaving group. The latter mechanism works under acidic conditions; however, this often requires excess acid and/or severe reaction conditions [8].We have recently shown [14] that [Ru(Cp*)(MeCN) 2 )(h 3 -PhCH=CHCH 2 )](PF 6 ) 2 ((Cp* = 1,2,3,4,5-pentamethylcyclopenta-1,3-dien-1-yl); 1) facilitates Friedel-Crafts type aromatic allylation reactions of phenols and related arene compounds under relatively mild conditions, using allyl carbonate substrates. There is now a modest literature involving metal-catalyzed Friedel-Crafts reactions [15], but little involving ruthenium [16]. We report here an extension of this chemistry and show that the dicationic catalyst precursor 1, which contains Ru IV rather than Ru II , affords the CÀC coupling products starting from a selection of alcohols, as indicated in Scheme 1. The Table gives a list of the substrates and products tested. The reactions were, in many cases, fairly rapid (often complete conversion in less than 20 min) and regioselective in that the attack occurred at the least-substituted allyl C-atom, and proceeded to completion under relatively mild conditions in MeCN solution. Several of the tested alcohols