C-13 NMR studies have shown that in both Pd(II)- and Pt(II)-allyl (modified-MOP) (MOP = (S)-2-diarylphosphino-1,1'-binaphthyl) complexes the substituent on the MOP auxiliary can affect how the naphthyl backbone interacts with a metal center. With the MeO-MOP analogue, the metal binds the carbon in a weak eta(1)-fashion, whereas with H-MOP it prefers an eta(2)-binding mode. For the Pt complexes, the (1)J(Pt-195,C-13) values proved to be diagnostic tools. Both modes of bonding afford relatively weak bonds to the metal. Modifying the MOP ligand structure from a PPh2 to a P(3,5-di-tert-butylphenyl)2 analogue can markedly affect the bond distances within the coordination sphere, as indicated by the X-ray structural data for PdCl(eta(3)-C3H5)(modified-MOP). 2-D NMR exchange spectroscopy can be used to recognize and distinguish between the two most common types of eta(3)-eta(1)-eta(3) isomerization process, i.e., rotation around the allyl C-C bond versus rotation around the allyl M-C bond. For the complex PdCl(eta(3)-C3H5)(H-MOP), the fastest isomerization process involves rotation around the allyl C-C bond.

The structural 3,5-dialkylphenyl effect on enantioselectivity is demonstrated for several Pd-catalyzed reactions including a ring-opening transmetalation, Heck arylation, and allylic alkylation. For these homogeneously catalyzed reactions the observed enantiomeric excesses (ee's) are found to improve by more than 15%. The ligands tested include MeO-Biphep and a P,N-phosphino-oxazoline-bidentate ligand containing 3,5-di-tert-butylphenyl substituents. Further, several derivatives of the monodentate auxiliary MOP ((R)-2-diarylphosphino-1,1'-binaphthyl) have been modified to include 3,5-dialkylphenyl substituents and these auxiliaries have been tested in Pd-catalyzed enantioselective hydrosilylation chemistry. For some, but not all of these MOP ligands, enhanced ee's of the order of 40-50% are found. Variable-temperature and 2-D NMR studies have been carried out on new model complexes and reveal selected restricted rotation around a number of the P-C(Ipso) aryl bonds. Solid-state structures for two of the new complexes, PdBr(p-NCC6H4)(phosphino-oxazoline, 2b), 8b, and PdCl(C6H4CH2NMe2)(MOP, 4b), 9b, have been determined.

A new set of Pd-MOP complexes (MOP = (S)-2-diarylphosphino-1,1'-binaphthyl) has been prepared. One of these, containing MeO-MOP (=2-(diphenylphosphino)-2'-methoxy-1,1'-binaphthyl), is shown to act as a chelating ligand with a naphthyl backbone diene bridging a Pd(I)-Pd(I) bond. This bonding mode exists in both the solid and solution states. A series of chloro-Pd(II)MOP complexes containing the well-known cyclometalated N V-dimethyl benzylamine chelate have been treated with NaBArF to extract the chloride ligand. The products, starting from the H-MOP, MeO-MOP, and NC-MOP analogues, are all different. Of particular interest is the product from the H-MOP reaction in that the fourth coordination position is occupied by a weak Pd-C sigma-bond from the naphthyl backbone, on the basis of C-13 NMR data. The rate of product formation in the Pd-catalyzed hydrosilylation of styrene with SiHCl3 has been measured as a function of time for the four auxiliaries H-MOP, MeO-MOP, HO-MOP, and NC-MOP. The NC-MOP is shown to be much faster than the others, and a tentative explanation is offered.

We show that both palladium(0) and palladium(II) metal centers are capable of coordinating two monodentate MOP (=(R)-2-(diarylphosphino)-1,1′-binaphthalene) ligands in a pseudo-cis orientation, despite published statements to the contrary. In addition to [Pd(η3-C3H5)(MeOMOP)2]BF4 (MeOMOP=(R)-2-(diphenylphosphino)-2′-methoxy-1,1′-binaphthalene), the first examples of chiral bis κC1-prop-2-enyl (η1-CH2CHCH2) complexes [cis-Pd(κC1-C3H5)2(MeOMOP or MOP)2], are shown to be relatively stable. Further, coordinated MOP and MeOMOP both show stronger propensity towards novel intramolecular π-olefin complexation than the CNMOP analogue. The solid-state structure of [Pd(fumaronitrile)(MOP)2] is reported.

The new Pd-MOP acetyl acetonate complexes [Pd(acac)(10a or 10b)]BF4, 12a,b, were prepared starting from [Pd(acac)(CH3CN)(2)]BF4, whereas [Pd(acac)(11-H)], 13, was obtained directly from Pd(acac)(2) by adding 11. [Ligand 10a, MeO-MOP = (R)-2-(diphenylphosphino)-2'-methoxy-1,1'-binaphthyl; ligand 11, HO-MOP = (R)-2-(diphenylphosphino)-2'-hydroxy-1,1'-binaphthyl]. The solid-state structures for cationic 12a and neutral 13 were determined via X-ray diffraction methods and reveal that both structures contain Pd-C sigma-bonds arising from the MOP naphthyl backbone. In structure 13, the hydroxyl function in 11 has lost a proton to afford a keto-anionic chelating ligand. C-13 NMR studies confirm that the solution structures are the same as those found in the solid state and, for 12, describe how the organic cation distributes the positive charge.

A phosphino,oxazoline P,N-bidentate ligand, 4, containing 3,5-di-tert-butylphenyl groups has been prepared. In the Heck arylation of dihydrofuran, 4 is shown to afford higher ee's than either 2 or 3, the unsubstituted and m-dimethylphenyl analogues, respectively. Several Pd(0) complexes of 4 are reported. The exchange dynamics of Pd(4)(dba) are shown to involve an interconversion of diastereomers via an intramolecular process. The X-ray structure for PdCl2(4), 8, was determined by X-ray diffraction methods. Comparison of data with PdCl2(2), 9, and PdCl2(3), 10, suggests that differing amounts of stacking influence the structures of these relatively simple Pd complexes, with 9 and 10 revealing the strongest, pi-pi interactions. An estimation of the van der Waals energies involved in the interaction supports a ca. 4 kcal/mol stabilization via pi-pi stacking.

The Pd‐catalysed enantioselective allylic alkylation of a 1,3‐diphenylallyl substrate using a bulky phosphinooxazoline auxiliary leads to a relatively small enantiomeric excess of 66%. The ca 30% loss, relative to related P,N‐auxiliaries, is rationalized by (a) the presence of additional isomers, (b) a dynamic equilibrium between two of these as shown by exchange spectroscopy and (c) the identification of one exchanging diastereomer in which there is almost no difference between the two terminal allyl 13C chemical shifts, i.e. these P‐ and N‐donors reveal an almost identical trans influence. Copyright © 2002 John Wiley & Sons, Ltd.

A series of cationic and dicationic Ru-arene complexes with Binap (1a) and MeO-Biphep (1b) have been prepared. 13C NMR studies are shown to be useful in connection with recognising the 6e-bonding mode of 1a and 1b in the dications [Ru(1a or 1b)(η6-arene)](SbF6)2 (8,9). Reaction of 8,9 with: (a) (Bu4N)(Ph3SiF2) leads to a cyclometallated product which arises via P—C bond breaking and P—F bond making; (b) methanol provides a straightforward synthesis of the corresponding hydrides. 13C NMR p-cymene chemical shifts are reported.Key words: P—C bond cleavage, 6e donors, cyclometallation, hydrides, 13C NMR.