Carbon-Phosphorus Couplings

Table 4.51. One-Bond (J and Longer-range (2J, 3J, 4J) Carbon-Phosphorus Coupling Constants of Representative Phosphines [372], Phosphonium Salts [365], Phosphine oxides [366, 372, 373], Phosphonium Ylides [365, 373], Phosphonates [368, 372], Phosphites [374], and Phosphates [375] (in Hz). 

Table 4.52. Structural Features and Carbon-Phosphorus Couplings [370 380] (in Hz).

Three-bond carbon-phosphorus couplings JCP depend on configuration, as expected, transoid couplings being larger than cisoid ones, as demonstrated for cyclohexyl- and 2-norbornylphosphonates in Table 4.52. The Karplus relation (4.13) can be derived from the data for 2-norbornyl derivatives [376]. 

Four-bound carbon-phosphorus couplings can also be resolved in some cases (Table 4.51). Carbon-phosphorus couplings transmitted by more than four bonds are detectable in n electron systems and have been reported for biphenylmethylphosphonates [368] and triphenylphosphabenzene, in which a 1JCP of 1 Hz can be resolved [370, 379]. 

Fig. 5.9. 13Cf1 - NMR spectrum of flavin adenine dinucleotide (FAD), disodium salt, 30 mg in 1 ml, of deuterium oxide 30 °C 100.576/400.133 MHz (13C/ H) 5000 interferograms (32K/15000 Hz) (a) sp3 carbon partial spectrum (20-92 ppm) with expanded output (b) to display carbon-phosphorus couplings (2JCI, for A5 and R5 3Jcr for A4 and R4 carbon nuclei) (c) partial spectrum of heterocyclic carbon nuclei (117-167 ppm). Signals are assigned according to ref. [147].

Formation of p-diketonato and monothio-P-diketonato derivatives The dihydrogen-ruthenium complex [Ru(t)5-C5H5)(CO)(ti2-H2) (P Pr3)]BF4 as a precursor for carbon-carbon, carbon-oxygen, carbon-nitrogen, carbon-sulfiir, and carbon-phosphorus coupling reactions... 

The K -NMR spectra were also consistent with this conformational analysis (Table VII). In flippii from a chair to a boat, the C-5— C-4—O—P torsional angle changes from trans to gauche. In 8a-11a, the carbon-phosphorus coupling constant Vjp is 8.8-9.8 Hz (trans), whereas in 11b, V5P is 6.1 Hz (gauche). In 8b- 11b, Vjp is intermediate (7.8 - 8.5 Hz), consistent with the rapid equilibration between chair and IxMit conformations. 

CARBON-PHOSPHORUS BOND-FORMING CROSS-COUPLINGS 386... 

Scheme 6.67 Palladium-catalyzed carbon-phosphorus cross-coupling.

This extremely air-sensitive compound, which is valence isoelectronic to an olefin, has been structurally characterized by X-ray diffraction. It has a short carbon-phosphorus double bond (1.62 A) the phosphorus and carbon atoms adopt a trigonal planar geometry with a dihedral angle of 60° (Fig. 3). This value is significantly larger than that reported for the most crowded olefin.61 Formally, this compound can be viewed as the product of a car-bene-carbenoid coupling between bis(trimethylsilyl)carbene and bis(diiso-propylamino)phosphenium triflate. Note that another route to methylene-phosphonium salt has been reported by Griitzmacher et al.62... 

THE DIHYDRIDE-OSMIUMaV) COMPLEX OsHjCljCPPrjlj AS A PRECURSOR FOR CARBON-CARBON, CARBON-NITROGEN, CARBON-PHOSPHORUS, CARBON-GERMANIUM, AND CARBON-SILICON COUPLING REACTIONS... 

Utility of Enol and Aryl Triflates. Enol and aryl triflates are extensively used for cross-coupling reactions, the formation of carbon-carbon, carbon-tin, carbon-nitrogen, carbon-sulfur, carbon-phosphorus, and carbon-halogen bonds, and reduction/ deoxygenation. In recent examples, they were used to form enamines or enamides or were eliminated to cyclooctynes for copper-free cycloadditions in biological systems. 

Carbon-phosphorus bonds may also be formed. Chemists at Merck developed a synthesis of either enantiomer of the valuable ligand BINAP 133 from the more easily resolved BINOL 2.612, using a triflate-phosphine coupling reaction (Scheme 2.183). They reasoned that nickel catalysis would be more effective as this metal is harder than palladium and, therefore, less susceptible to catalyst poisoning by the product. BINAP 133 could be obtained with no loss of chirality. They also reported a resolution procedure for BINOL 2.612.224... 

Two- and three-bond carbon-phosphorous and the corresponding proton-phosphorus couplings have been measured by Haire et al for several phosphorus reagents and their silyl derivatives. 

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