Phosphorus—Carbon Links

Aromatic. Daasch and Smith [5] have examined a considerable series of aryl phosphorus compounds containing the P-aryl group, and have found in all cases bands in the regions 1450— 1435 cm and 1005—995 cm which are sharp and of moderate intensity. They associate these with the P-phenyl link, but point out also that they might equally well arise from ring vibrations which 

Aliphatic. No useful correlations for the P—C linkage have been formulated, and as the P—C stretching bands of compounds such as trimethyl phosphine oxide [15] appear to lie in the 750—650 cm range in which many other types of organo-phosphorus compounds also absorb, it is doubtful whether any such correlations could be developed. 

No useful correlations exist for other P—alkyl groups. The 

P—O—Ethyl group has one or two weak bands in the 1250 cm region, but they are not sufficiently strong or sufficiently characteristic to be of value. 

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Hydrogen atoms on the carbon linked to phosphorus are acidic enough to protonate the oxygen atom of the carbonyl group while the rest of the... 

The coordination chemistry of compounds containing phosphorus-carbon multiple bonds, such as phosphaalkynes, phosphaalkenes, phos-phaallenes, phosphaalkenyls, and phosphaallyls, has been studied extensively (349,350). The chemistry is dominated by the donor properties of the phosphorus atom, and, as far as we are aware, no examples of bimetallic or trimetallic compounds with bridging ligands which link metal centers by a carbon cr bond and a C=P or C P n bond have been recorded. Once the lone pair on the phosphorus atom is involved in bonding, the unsaturated bond becomes a possible site for further coordination. 

The common link between the two areas of research mentioned above (carbon cages and polycyclic phosphanes) is provided by the phosphorus-carbon cage compounds — the topic of the present chapter. In accord with the philosophy of this book, we will concentrate mainly on the results from our own laboratories and outline their position in the wider perspectives... 

Ultimately, those factors which influence the outcome of the WEH reaction are linked to, and are a measure of, the stability of the phosphorus-carbon bond in equilibria between carbanion and carbonyl reactant. In general, dialkyl phosphonate carbanions (162 R = EtO) in their reactions with either aliphatic or aromatic aldehydes yield (E)-alkenes, whereas carbanions based on the l,3,2-dioxaphosph(V)olane 163 (X = O) or the 1,3,2-dioxaphosphorinane ring 164 (X = O) mav reverse the relative amounts of the (Z)- and (E)-alkenes, in this case from ca 1 2 to ca 2 1 no reaction at all was observed in this instance... 

It should be noted that these N-phosphines are not organometallic from the point of view of this volume until they form phosphomum compounds, for only in the latter case is the phosphorus directly linked to carbon... 

It has generally been assumed that the bonds that link the catalyst to the polymer support are chemically stable under the reaction conditions one employs. Until recently, the literature offered little information in this regard, since lifetime studies are needed to properly evaluate stability. Recent publications have pointed out the chemical instability of the phosphorus-carbon bond of tertiary phosphine functionalized supports and the chemical reactivity of various nitrogen functionalized polymeric support materials under reaction conditions. If such chemical stability problems are present, the consequences are indeed serious. While a typical "leach" situation would necessitate a periodic reloading of the metal complex, cleavage of polymer functionality would necessitate replacement of both the metal complex and the polymer. 

The following sections summarize only the most prominent interactions between the elemental cycles and the links in the hydrologic cycle. Water also plays a role in many chemical and biological reactions that are beyond the scope of this discussion. The carbon, nitrogen, sulfur, and phosphorus cycles are discussed in detail in Chapters 11, 12, 13, and 14, respectively. 

Examples of reactions involving replacement and cyclization are the long-known preparation of thiophenes (89) from 1,4-diketones, and the formation of l,2-dithiole-3-thione (90) from the salicylate ester analog (91).120 In the latter instance, oxidative cyclization with formation of an S—S bond has occurred this is a common feature of these reactions, particularly if such a link is needed to complete a five-membered ring. Another example of this aspect is afforded by the reaction of the propane-1,3-dione derivatives (92) which yield 3,5-diaryl-1,2-dithiolylium salts (93) when heated with phosphorus pentasulfide in carbon disulfide, followed by perchloric acid.121... 

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