Samantha C. Reynolds
Published: 2012
Total Pages: 826
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Introduction. This chapter provides a brief overview of the thesis. Chapter 1: tert-butyl-diphosphabutarene - Synthesis and reactivity of a novel phosphacycle. Treatment of 1,2-bis(dichlorophosphino)benzene (12) with tert-butylmagesium chloride followed by magnesium powder cleanly forms the air-stable phosphacycle C6H4(P(t-Bu))2 13 as a racemic mixture. Recrystallization of the Pd complex 23, derived from {Pd[(S)-Me2NCH(Me)C10H6]([mu]-Cl)}2, resulted in separtion of diastereomers, which furnished highly enantioenriched 13 on removal of the Pd fragment with dppe (1,2-bis(diphenylphosphino)ethane). Additions across the P-P bond of enriched 13 gave bis(tertiary) phosphines, such as BenzP*. The synthesis, diastereomeric separation via 23, and reactivity of 13 is discussed. Chapter 2: Effect of linker length on the selectivity of pt-catalyzed asymmetric alkylation of Bis(phenylphosphino)alkanes. As part of a broader study of Pt-catalyzed asymmetric alkylation of bis(secondary phosphines), PhHP(CH2)[subscript-n]PHPh (n=2-6), with benzyl bromide, the selectivity of alkylation for substrates with n=2 and n=5 was investigated. For n=3-5, the reaction is catalyst-controlled, whereas the alkylation of PhHP(CH2)2PHPh is substrate controlled. The extent of substrate control in the alkylation of PhHP(CH2)2PHPh is discussed, in addition to the possible structural and mechanistic reasons for this difference in selectivity. Chapter 3: Synthesis and reactivity of bis(secondary phosphines) containing rigid phenylene and quinoxaline backbones. The synthesis and alkylation of several bis(secondary phosphines) containing rigid linkers was attempted. The bis(secondary phosphinobenzenes) 1,2-C6H4(PHR)2 (R=t-Bu (4), Mes (5)) were prepared, but did not undergo selective alkylation with benzyl bromide under a variety of conditions. Quinoxaline-based bis(secondary) phosphines 22a-c were synthesized as part of a mixture, but could not be isolated for further studies. Chapter 4: Synthesis and structure of transition metal-menthyl complexes. A Grignard reagent derived from ( - )-menthyl chloride has been reported to be a 1:1 mixture of menthyl magnesium chloride and neomenthyl magnesium chloride. As part of a broader study, addition of an excess of this Grignard to the metal chloride complexes Au(PPh3)(Cl), Pt(dppe)Cl2 (dppe=Ph2PCH2CH2PPh2), or Pt(dppen)Cl2 (dppen=cis-Ph2PCHCHPPh2) gave Au(PPh3)(Men) (Men=menthly), Pt(dppe)(Men)(Br), and Pt(dppen)(Men)(Br), respectively. This chapter describes the characterization of Au(PPh3)(Men) by 1D and 2D miltinuclear NMR and details the degradation of the Au and Pt complexes in chloroform. Chapter 5: Trans-selective ring opening of limonene oxide with phosphine nucleophiles. Treatment of a 1:1 mixture of cis-and trans-limonene oxide with half an equivalent of lithium primary phosphido nucleophile results in selective attack at the epoxide of the trans-isomer to afford chiral secondary phosphines. Futher reaction of the secondary phosphines may provide a catalogue of P-stereogenic/C-stereogenic tertiary phosphine ligands. The characterization of these phosphines and highly modular nature of the synthesis will be discussed.