Introduction: This chapter provides a brief overview of the thesis. Chapter 1: Pt-Catalyzed Asymmetric Alkylation of Bis(isitylphosphino)ethane: P-benzyl Bond Formation Induces a Reversal of Catalyst Selectivity. Asymmetric alkylation of IsHP(CH2)2PHIs (1, Is = 2,4,6-(i-Pr)3C6H2) with 2-bromomethylnaphthalene in the presence of NaOSiMe3 and the catalyst precursor Pt((R,R)-Me-Duphos)(Ph)(Cl) (2) selectively gave meso-Is(CH2-2-naphthyl)P(CH 2)2P(CH2-2-naphthyl)Is (3) (diastereomeric ratio (dr), meso:rac = 3:1). After oxidation of 3 to the bis(phosphine oxide) 3-O2, chiral HPLC and 31P NMR spectroscopy using a chiral shift reagent, FmocTrp(Boc)-OH (7), were independently used to measure its dr and er (enantiomeric ratio). With similar data for catalytic alkylation of IsHP(CH2) 2P(CH2-2-naphthyl)Is (4), the selectivity of both alkylations of 1 could be calculated, revealing that catalyst selectivity is reversed after the first alkylation. The change observed is attributed to strong negative cooperativity or substrate control where the stereochemistry of the first alkylation influences the selectivity of the second alkylation. For comparison to 3 and 4, the selectivity of Pt-catalyzed asymmetric alkylation of the monophosphine substrates PHIs(CH2)2X (X = OSiMe3 ( 21); OH (31); OSi(i-Pr)3 ( 32)) was determined. Variation in the size of the X groups had small effects on alkylation. This shows that both absolute configuration and its substituent three bonds away from the site of alkylation (γ position) affect the selectivity of catalysis.
Chapter 2: Effects of Linker Length on Rate and Selectivity of Platinum-Catalyzed Asymmetric Alkylation of the Bis(isitylphosphino)alkanes IsHP(CH2)nPHIs (Is = 2,4,6-(i -Pr) 3C6H2, n = 1-5). Asymmetric alkylation of IsHP(CH2)nPHIs (1-5, n = 1-5, Is = 2,4,6-( i-Pr) 3C6H2) with benzyl bromide in the presence of NaOSiMe3 and the catalyst precursor Pt(( R,R)-Me-Duphos)(Ph)(Cl) (6) gave Is(CH2Ph)P(CH 2)nP(CH2Ph)Is (7-11, n = 1-5) with rate and selectivity that was dependent on n. Oxidation to the bis(phosphine oxides) 7-11-O2 allowed determination of the er (enantiomeric ratio) and dr (diastereomeric ratio) using 31P NMR spectroscopy and a chiral shift reagent, FmocTrp(Boc)-OH (12). Comparison of the dr and er to predictions based on catalyst control suggested that alkylation of 4-5was catalyst controlled, while that for 1-2was under substrate control. The selectivity of asymmetric alkylation of IsHP(CH 2)3P(CH2Ph)Is (13) enabled determination of the selectivity of both alkylations of 3 revealing that selectivity was weakly substrate controlled. This provides a striking contrast to the substrate control for 2. Comparing these results to those for the analogous substrates, PhHP(CH2) nPHPh (n = 2-6), showed that selectivity was dependent on linker length and P-substituent.
Chapter 3: Synthesis, Structure, Dynamics, and Selective Alkylation of Platinum and Palladium Diphosphametallacyclobutane Complexes. The mononuclear diphosphametallacyclobutane complexes, M(dppe)(IsPCH2PIs) (M = Pd (1); M = Pt (2)), or Pt((R,R)-Me-DuPhos)(IsPCH 2PIs) (3), were prepared by treatment of M(dppe)Cl 2 (M = Pt, Pd) or Pt((R,R)-Me-DuPhos)Cl2 with IsHPCH2PHIs and two equiv of NaOSiMe3. Dynamic processes involving phosphorus inversion and rotation about the P-C(Is) bonds in 1-3 were characterized by variable temperature NMR spectroscopy, and 1-3 were structurally characterized by X-ray crystallography. The catalyst precursor Pt((R,R)-Me-DuPhos)(Ph)(Cl) mediated alkylation of secondary phosphines in the presence of NaOSiMe3 to yield the bis(tertiary) phosphine IsMePCH2PMeIs (10) either from PHMe(Is) and CH2I2 or from IsHPCH2PHIs and MeI. Treatment of 1-3 with two equiv of methyl triflate gave the dications [M(dppe)(IsMePCH2 PMeIs)][OTf] 2 (M = Pd, 4; M = Pt, 5) and [Pt((R,R)-Me-DuPhos)(IsMePCH 2PMeIs)][OTf] 2 (6) via the observable intermediates mono-methylated [M(diphos)(IsMePCH2PIs)][OTf] (M = Pd, diphos = dppe, 7; M = Pt, diphos = dppe, 8; M = Pt, diphos = (R,R)-Me-DuPhos, 9). These methylations gave Me-DuPhos complex 6 almost exclusively as a single C 2-symmetric diastereomer, but a mixture of rac and meso diastereomers was formed for dppe complexes 4-5. Treatment of M(dppe)(OTf)2 or Pt((R,R)-Me-DuPhos)(OTf) 2 with meso-10 rac- 10 selectively gave meso or rac-[M(diphos)(IsMePCH 2PMeIs)][OTf] 2 (11-13).
Chapter 4: Structure Determination of a Gold Phosphido Complex by Solution-State NMR Spectroscopy and X-ray Crystallography. The gold phosphido complex, [AuP(Mes)(CH2)3(Mes)PAu] 4 (Mes = 2,4,6-(Me)3C6H2, 1), prepared by Elizabeth Lane, was structurally characterized by NMR spectroscopy and X-ray crystallography. The structure contains a cube of phosphorus atoms and an Au8P8 core with idealized D2d-symmetry that was predicted by NMR spectroscopy, including DOSY studies, and confirmed by X-ray crystallographic structure determination.