Phosphorus bonding types

Many types of phosphorus-phosphorus bonds are known, but it is rare to find such bonds in hexacoordinated phosphorus compounds (with the exception of 57). Cavell reported in 1998 the reaction of PCI5 with phenylbis(o-(trimethyl-siloxy)phenyl)phosphane, yielding the corresponding bischelate 61 in decent yield (52%) [99]. The octahedral nature of the central phosphorus atom was unambiguously determined by X-ray structural analysis. Two short axial bonds (2.202 A) lie perpendicular to the pseudo-octahedral equatorial plane. 

New aluminophosphate oxynitrides solid basic catalysts have been synthesised by activation under ammonia of an AIPO4 precursor. When the nitrogen content increases, XPS points out two types of nitrogen phosphorus bonding. The conversions in Knoevenagel condensation are related to the surface nitrogen content. Platinum supported on aluminophosphate oxynitride is an active catalyst for isobutane dehydrogenation. 

Our focus is on the most comprehensively studied series, the monophosphides of the first-row transition metals, whose structures successively distort from NaCl-type (ScP) to TiAs-type (TiP), NiAs-type (VP), MnP-type (CrP, MnP, FeP, CoP), and NiP-type, forming stronger metal-metal and phosphorus-phosphorus bonding with greater electron count (Fig. 11) [63-65], The P atoms are six-coordinate, but... 

In this chapter, we first review the nature of the several forms of elemental phosphorus and then proceed to consider their uses for specific types of syntheses of compounds containing the carbon-phosphorus bond. Prior reviews have also been concerned with these topics.1 2 Our purpose here is to update these presentations and provide fundamentals for the practicing chemist venturing into the use of elemental phosphorus. We limit this discussion to the more-or-less direct syntheses of organophosphorus compounds from elemental phosphorus. We will consider reactions that generate monophosphorus species without C-P bonds as critical intermediates, pro-... 

Intramolecular alkyl transfer is a fundamental problem with this reaction this problem can be addressed with modification in structure of the reagents. Neutral trivalent phosphorus reagents do react with carbonyl compounds at much lower temperatures, but lead to several types of pentacoordinated phosphorus products.190-198 More will be noted about the use of such pentacoordinated phosphorus species for carbon-phosphorus bond formation in Chapter 5. 

The aromaticity of the phosphorus compounds with the A—D bonding type (shown in Scheme 1) will be discussed below, using structural, energetic, and magnetic criteria. The chemical reactivity—in relation to the aromatic stabilization—will be mentioned as well. 

In 1995 a breakthrough occurred in this field in February we were able to show the synthesis and the spectroscopic properties of the first complexes of type B [7], and in August the first isolated and structurally characterized complexes containing terminal metal-phosphorus triple bonds (type A) were independently obtained and published in back-to-back articles by the groups of Cummins [8] and Schrock [9]. Since then, a rapid development has occurred in the synthesis and particularly in the study of the reactivity pattern of complexes with phosphorus-transition metal triple bonds. This review chapter will highlight the development in this field by giving an overview from 1995 until the current stage of research. 

Before 1964 no stable compound with a localized or delocalized carbon-phosphorus double bond was known. Indeed, it was generally assumed that the atomic radius of phosphorus, being larger than that of carbon or nitrogen, would not provide sufficient 2pn—3pir overlap for such a ir system to be stable Our first communication, written jointly with Peter Hoffmann which described the synthesis of a stable phosphamethin-cyanine 1 with a delocalized P—C double bond was therefore received with skepticism However, after Allmann confirmed the structure by X-ray analysis the existence of a new type of phosphorus bond in a cationic delocalized tt system was unambigously established... 

To illustrate the potential diversity of structure and bonding of phosphorus, the classic Lewis representations for each possible coordination number one to six are shown in Fig. 15.4.1. Many of these bonding types have been observed in stable compounds, which are discussed in the following sections. 

Pregosin and co-workers have shown that a detailed analysis of the trends in coupling and chemical shifts can be a valuable asset in determining the symmetry of a variety of Pd(2 +) and Pt(2 +) complexes. For example, in complexes of the type PdCl2La Ca in the ligand usually lies to lower field in the cis complex than in the trans complex while the para resonance in a phosphorus bonded phenyl ring is found at lower field in the trans complex than in the cis (80, 84). 

To promote the formation of the rather weak silicon-phosphorus bonds, we have introduced anionic monophosphinomethanide and diphosphinomethanide ligands of type I or II (Fig. 1), respectively, into the coordination sphere of a silicon center. 

Hexacoordinated phosphorus species bearing a formal positive charge have been generated, albeit without a carbon-phosphorus bond. Rather, compounds of the type for which an example is shown as (16) have been prepared with four oxygen and two nitrogen ligands with an overall positive charge. ... 

We wish to report several metal complexes formed from a phosphorous acid diester of the type OP (H) (OR) 2 which underwent isomerization to form a metal-phosphorus bond as in (a). In the course of our investigations on the complexing properties of polycylic phosphites (9 17) j it was found that 2,8,9-trioxa-l-phosphaadamantane (L) undergoes a rapid, acid hydrolysis in acetone to form two colorless, crystalline hydrolysates, A and B. Only isomer A or L complexed with divalent hydrated metal ions, and it is concluded from infrared evidence that A has isomerized as shown in the following reaction sequence. Supporting infrared and PNMR evidence is presented for the tentatively postulated structures of A and B. 

The phosphonitrilic halides are weaker bases than are some related nonaromatic compounds, just as pyridine is a weaker base than piperidine. The bond type in the phosphonitrilic series is probably the same as in the phosphine-imines RaPrNR (80, 81) the stability of these compounds, too, increases with the electronegativity of the substituents on the phosphorus. Tetraphenylphosphine-imine is one of the most stable of these compounds, and forms a hydrochloride. Its base strength is therefore greater than those of the phosphonitrilic halides, presumably because the opportunities for electronic delocalization are less. The Af-ethyl ester of the trimeric phosphonitrilic acid, which has a cyclic structure, but in which resonance of the same type as in the phosphonitrilic halides cannot occur, also forms a hydrochloride ( 1). It is, therefore, a comparatively strong base, in spite of the inductive effect of the two oxygen atoms on the phosphorus. The extreme weakness of the phosphonitrilic halides as bases cannot therefore be wholly due to the inductive effect of the halogens. 

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