The complexes Pd(diphos)(o-An)(I) (o-An = o-MeOC6H4; diphos = dppe (3), (S,S)-Chiraphos (4), (R,R)-Me-Duphos (5), (R,S)-t-Bu-Josiphos (6), (R)-Tol-Binap (7)) were prepared. Complex 6 catalyzed the coupling of PH(Me)(Ph)(BH3) (2) with o-AnI in the presence of base to yield PAMP−BH3 (P(Me)(Ph)(o-An)(BH3) (1)) in low enantiomeric excess. The course of stoichiometric reactions of 3−7 with 2 and NaOSiMe3 depended on the diphosphine ligand. Complexes 6 and 7 gave PAMP−BH3 (1) and Pd(0) species; no intermediates were observed. With 3, the intermediate Pd(dppe)(o-An)(P(Me)(Ph)(BH3)) (10) was observed by 31P NMR, while 4 gave the isolable diastereomeric palladium complexes (S P )-Pd((S,S)-Chiraphos)(o-An)(P(Me)(Ph)(BH3)) (11a) and (R P )-Pd((S,S)-Chiraphos)(o-An)(P(Me)(Ph)(BH3)) (11b), whose absolute configurations were determined by X-ray crystallography after separation. The analogous Pd((R,R)-Me-Duphos)(o-An)(P(Me)(Ph)(BH3)) diastereomers (12a,b) were also separated and isolated. Treatment of 4 with highly enantioenriched 2 (R or S) gave 11a or 11b in high diastereomeric excess with retention of configuration at phosphorus. P−C reductive elimination from either isomer of highly diastereoenriched 11 in the presence of excess diphenylacetylene yielded Pd((S,S)-Chiraphos)(PhC⋮CPh) (14) and highly enantioenriched PAMP−BH3 (1), with retention of configuration.

The chiral Pd(0) trans-stilbene complexes Pd(diphos*)(trans-stilbene) (diphos* = (R,R)-Me-Duphos, (R,R)-Et-Duphos, (R,R)-i-Pr-Duphos, (R,R)-Me-BPE, (S,S)-Me-FerroLANE, (S,S)-Me-DuXantphos, (S,S)-Et-FerroTANE, (R,S)-CyPF-t-Bu, (R,S)-PPF-t-Bu, (R,S)-BoPhoz) and Ni((R,R)-Me-Duphos)(trans-stilbene) were prepared by NaBH(OMe)3 reduction of the corresponding M(diphos*)Cl2 compounds in the presence of trans-stilbene. The rate of oxidative addition of phenyl iodide to the stilbene complexes, which gave Pd(diphos*)(Ph)(I), depended on the ligand (larger for increased ligand bite angles and reduced steric bulk) and was markedly faster than oxidative addition to mixtures of Pd(dba)2 and diphos*. The complexes Pd(diphos*)(Ph)(I) were prepared independently by treatment of PdL2(Ph)(I) (L2 = TMEDA, (PPh3)2) with diphos*. Oxidative addition of PhI to the complexes M((R,R)-Me-Duphos)(trans-stilbene) occurred in the rate order Pd > Ni ≫ Pt. The complexes Pd(diphos*)Cl2, Pd(diphos*)(trans-stilbene), and Pd(diphos*)(Ph)(I), as well as some analogous Ni compounds, were structurally characterized by X-ray crystallography.

Asymmetric cross-coupling of aryl iodides (ArI) with secondary arylphosphines (PHMe(Ar'), Ar' = (2,4,6)-R3C6H2; R = i-Pr (Is), Me (Mes), Ph (Phes)) in the presence of the base NaOSiMe3 and a chiral Pd catalyst precursor, such as Pd((R,R)-Me-Duphos)(trans-stilbene), gave the tertiary phosphines PMe(Ar')(Ar) in enantioenriched form. Sterically demanding secondary phosphine substituents (Ar') and aryl iodides with electron-donating para substituents resulted in the highest enantiomeric excess, up to 88%. Phosphination of ortho-substituted aryl iodides required a Pd(Et-FerroTANE) catalyst but gave low enantioselectivity. Observations during catalysis and stoichiometric studies of the individual steps suggested a mechanism for the cross-coupling of PhI and PHMe(Is) (1) initiated by oxidative addition to Pd(0) yielding Pd((R,R)-Me-Duphos)(Ph)(I) (3). Reversible displacement of iodide by PHMe(Is) gave the cation [Pd((R,R)-Me-Duphos)(Ph)(PHMe(Is))][I] (4), which was isolated as the triflate salt and crystallographically characterized. Deprotonation of 4-OTf with NaOSiMe3 gave the phosphido complex Pd((R,R)-Me-Duphos)(Ph)(PMeIs) (5); an equilibrium between its diastereomers was observed by low-temperature NMR spectroscopy. Reductive elimination of 5 yielded different products depending on the conditions. In the absence of a trap, the unstable three-coordinate phosphine complex Pd((R,R)-Me-Duphos)(PMeIs(Ph)) (6) was formed. Decomposition of 5 in the presence of PhI gave PMeIs(Ph) (2) and regenerated 3, while trapping with phosphine 1 during catalysis gave Pd((R,R)-Me-Duphos)(PHMe(Is))2 (7), which reacted with PhI to give 3. Deprotonation of 1:1 or 1.4:1 mixtures of cations 4-OTf gave the same 6:1 ratio of enantiomers of PMeIs(Ph) (2), suggesting that the rate of P inversion in 5 was greater than or equal to the rate of reductive elimination. Kinetic studies of the first-order reductive elimination of 5 were consistent with a Curtin-Hammett-Winstein-Holness (CHWH) scheme, in which pyramidal inversion at the phosphido ligand was much faster than P-C bond formation. The absolute configuration of the phosphine (SP)-PMeIs(p-MeOC6H4) was determined crystallographically; NMR studies and comparison to the stable complex 5-Pt were consistent with an RP-phosphido ligand in the major diastereomer of the intermediate Pd((R,R)-Me-Duphos)(Ph)(PMeIs) (5). Therefore, the favored enantiomer of phosphine 2 appeared to be formed from the major diastereomer of phosphido intermediate 5, although the minor intermediate diastereomer underwent P-C bond formation about three times more rapidly. The effects of the diphosphine ligand, the phosphido substituents, and the aryl group on the ratio of diastereomers of the phosphido intermediates Pd(diphos*)(Ar)(PMeAr'), their rates of reductive elimination, and the formation of three-coordinate complexes were probed by low-temperature 31P NMR spectroscopy; the results were also consistent with the CHWH scheme.

Treatment of Pd((S,S)-Chiraphos)(o-An)(I) (3, o-An = o-MeOC6H4) with either enantiomer of highly enantioenriched PH(Me)(Ph)(BH3) (1) gave the phosphido-borane complex Pd((S,S)-Chiraphos)(o-An)(P(Me)(Ph)(BH3)) (4) with retention of configuration at phosphorus, as shown by X-ray crystal structure determinations for both diastereomers of 4. Heating either diastereomer of 4 with diphenylacetylene gave Pd((S,S)-Chiraphos)(PhCCPh) (5) and P(o-An)(Me)(Ph)(BH3) (2) with retention of configuration at phosphorus.

A series of [MCpRTp] n + (CpR = Cp*(pentamethylcyclopentadienyl) or Cp (cyclopentadienyl), Tp = hydrotris(pyrazolyl)borate) complexes have been synthesized by reaction of a suitable MCpR precursor with KTp (CpR = Cp*; n = 0, M = Cr, Fe, Co, Ni; n = 1, M = Cr, Co, Ni; CpR = Cp; n = 0, M = V, Co, Ni; n = 1, M = V, Co). Oxidation with [FeCp2]+ salts or reduction with CoCp2 where appropriate provided easy access to the corresponding M(III) or M(II) species. All of the complexes studied showed reversible M(III)/M(II) redox couples. Similarly [MCpRTpm] n + complexes have also been isolated (Tpm = hydrotris(pyrazolyl)methane; CpR = Cp*, n = 1, M = Fe; CpR = Cp, n = 1 or 2, M = Co). Analytical, NMR, IR, and mass spectroscopic data are consistent with the formulation of these species as mixed-sandwich complexes. Oxidation of VCpTp in MeCN solution yields [VCpTp(MeCN)]+, whereas similar reaction in CH2Cl2 solution yields [VCpTp]+. [VCpTp]+ reacts with σ-donor ligands L, where L = CNtBu and PMe3, to form [VCpTpL]+ species, but is unreactive when L = CO, indicating little π-base character to the V center. Crystal structure determinations were performed for various complexes:  CoCp*Tp is unique in displaying κ2-Tp and η5-Cp* coordination, whereas [VCpTp]+, [CoCp*Tp]+, NiCp*Tp, and [CoCpTpm]2+ all display mixed-sandwich structures with κ3-Tp binding. The factors determining the relative conformations of the CpR and Tp ligands are discussed. The structures of [VCpTp(MeCN)]+ and [VCpTp(PMe3)]+ were also determined and show that considerable distortion of the sandwich moiety has occurred to accommodate coordination of the extra ligand. For the MCpRTp complexes a dependence of νB - H on Tp hapticity, ancillary ligand, and oxidation state is observed from IR spectroscopic data in the solid state. IR data obtained in solution suggest that CoCp*Tp is in conformational equilibrium, with a κ3-Tp structure also present. Some of the factors affecting 1H and 13C NMR shifts are discussed and compared with relevant homoleptic analogues. Electrochemical data reveal, in general, that MCp2 and MCp*2 species are more electron rich, although comparisons are best confined to a per metal basis.

Enantioselective or diastereoselective intramolecular cyclization of functionalized secondary phosphines or their borane adducts catalyzed by chiral Pd(diphosphine) complexes gave P-stereogenic benzophospholanes in up to 70% ee. These results provide a new method for the synthesis of chiral phospholanes, which are valuable ligands in asymmetric catalysis. [reaction: see text]

Re(CO)3L compounds, where L is a methane-derivatized tripodal ligand, can be prepared under aqueous conditions, and one of which displays significant stability under physiological conditions.

The syntheses of the 4-coordinate Tp'MCl complexes (where M = Fe (1), Mn (2); and Tp' = hydrotris(3-isopropyl-4-bromopyrazolyl)borate) are described. The single-crystal X-ray structures show that the metal centers have distorted tetrahedral coordination. Analogous reaction of CrCl(2)(MeCN)(2) with TlTp' gave Cr(kappa(3)-Tp')(kappa(2)-Tp') (3) as the initial product. The 5-coordinate structure was assigned by single-crystal X-ray crystallography, and it was found that the kappa(3) ligand had isomerized to hydro(3-isopropyl-4-bromopyrazolyl)(2)(5-isopropyl-4-bromopyrazolyl)borate). 3 is labile in solution: in pentane it slowly converts to the 6-coordinate isomer Cr(kappa(3)-Tp')(2) (4), whose structure was determined by X-ray crystallography. In 4 both ligands are isomerized. Both 3 and 4 display Jahn-Teller distorted structures expected for high-spin d(4) configurations. Variable temperature magnetic susceptibility measurements confirm that 1, 2, and 3 all have high-spin electronic configurations in the range 5-300 K. In benzene solution 3 decomposes; one product [Cr(kappa(3)-Tp')(2)](+)[Tp'](-) (5), was identified by X-ray crystallography. 5 contains a pseudooctahedral Cr(III) cation with both ligands in the isomerized form and an uncoordinated Tp' ligand as counterion. Mechanistic studies reveal that this reaction is light rather than heat induced. IR spectroscopy is utilized to confirm the ligand hapticity in all complexes from the value of nu(B)(-)(H), and comparison is made with similar compounds.