Phosphaethyne

Reaction of (diisopropylamino)phosphaethyne P=CN(Pr )2 with [Ni(CO)3(P C6Hn 3)] affords the planar 16-electron Ni° complex (1056) with -bound phosphaethyne.2540 Upon coordination, the P=C triple bond distance increases to 1.665(2) A, which is typical for phosphaalkenes. Upon... 

Scheme 6 Regiospecific [3+2] cycloaddition of phosphinodiazomethane with phosphaethyne...

The reaction of the lithium bis(trimethylsilyl)arsenide (47) with -butyl phosphaethyne (45) <89TH 423-01,93PS(77)45,94JOM(480)45> or a phosphaalkene precursor thereof (46) leads to a mixture of lithium 1,2,4-triphospholide, 1,2,4-diphosphaarsolide (48) and 1,4,2-diphosphaarsolide (49) (Scheme 11). 

The extremely sterically hindered 1,2,4-diazaphospholes 139-142 were prepared via [2+3] cycloaddition reaction of 2-(2,4,6-tri-/,< +-butylphenyl)-l-phosphaethyne 138 with trimethylsilyldiazomethane derivatives (Scheme 11). Structures of 1,2,4-diazaphospholes 140 and 142 were investigated by NMR spectroscopy and X-ray diffraction. The experimental structural studies as well as theoretical calculations confirmed aromatic character of these 1,2,4-diazaphospholes. The crystal structure of compounds 140 and 142 showed remarkable hydrogen bonding character in relation to molecular aggregation due to the presence of the bulky aryl groups <2007EJI3491>. 

Compound 1 was also used in the preparation of various l-trimethylsilyl-2-trimethyl-silyloxy-l-phosphethenes and phosphaethynes by the condensation-silatropy method 18 and condensation-silatropy-elimination method , respectively (Scheme 4)19. 

Reaction of 1 with 2,4,6-tri-t-butylbenzoyl chloride formed a 2,3-diphosphabuta-l,3-diene as well as a phosphaethyne (equation 5)20. An amino-substituted phosphaethyne was prepared starting from 1 and isopropyl isocyanate by an addition-elimination-silatropy reaction (equation 6)21. Addition of 1 to kinetically stabilized phosphaketene (see Section HI) gave a 1 1 adduct22 or a 1 2 adduct23 the former was converted to 1,3-diphospha-buta-1,3-dienes by treatment with acyl chlorides (equation 7)22. Both adducts could be converted to the same 1,2,4-triphosphabuta-l,3-diene23,24. 

Reactions of lithium bis(trimethylsilyl)phosphide (5) have recently been reviewed11. Some reports have been published concerning the structure of 559. Compound 5 was used in the preparation of phosphaethenes and phosphaethynes (equation 37 and Scheme 4)28 31. Reaction of 5 with benzophenone led to the observation of a signal probably due to Me3SiP=CPh231. Treatment of 5 with carbon disulfide and then chlorotrimethylsilane afforded a thiadiphosphole derivative (equation 38)60. Reaction of LiP(SiMe3)2 DME with a thiuronium iodide formed a phosphaethene (equation 39)61. 

Acyl(trimethylsilyl)phosphide, another example of mono(trimethylsilyl)phosphide, was converted to phosphaethene or phosphaethyne (equation 49)19. By a similar method mentioned in Section II.B.2, phosphino- or germyl-substituted phosphasilenes were prepared starting from RP(H)—Si(F)Tip2 via RP(Li)—Si(F)Tip2 (equation 50)63. Furthermore, a metallophosphasilene was generated as shown in equation 5171. 

In the following, three comparisons of isoelectronic systems are presented. The first consists of a comparison of the isoelectronic ligands ethyne (HCCH) and phosphaethyne (HCP) for different transition metals and in different states of aggregation. The second compares cyclopenta-dienyl and pentadienyl complexes, while the third relates complexes of benzene and hexaphosphabenzene. Although narrow in terms of breadth of compounds, we hope there is sufficient detail in these systems to convey some appreciation of the systematic variation possible with isoelectronic substitution. 

Co-condensation of indium vapor and tert-butyl-phosphaethyne at 77 K yields the volatile ln(l) complexes [In(jj -P3C2Bu2)] and 1,3-diphosphacyclopentadienyl complex [In(j7 -P2C3Bu3)]. Single-crystal x-ray diffraction studies for [In(jj -P3C2Bu9] reveals a discrete molecular stmcture, involving half-sandwich coordination of the... 

Protonation of nonmetal-0 multiple bonds, in phosphaethynes or phospha- or arsaethenes ... 

A theoretical study of the intermediates involved in the formation of phospha-propyne from pyrolysis of vinylphosphirane has led to a new route to phospha-alkynes. Thus, pyrolysis of trimethylsilyl(l-phosphiranyl)diazomethane has yielded MeaSiC = P, via an intermediate 1-phosphiranylmethylene . Regioselec-tivity in the [3 + 2] cycloaddition reaction between phosphaethyne and diazomethane has been studied by theoretical techniques , and further examples of reactions of this type described . Cycloaddition of phospha-alkynes with silylenes has also been reported. The primary phosphine 324 has been isolated from the addition of diethylphosphite to t-butylphosphaethyne. The chemistry of phospha-alkyne cyclotetramer systems has been reviewed and the first examples of platinum(II) complexes of such cage systems described. Aspects of the reactivity of coordinated phospha-alkynes have received further study, and a remarkable metal-mediated double reduction of t-butylphosphaethyne to the complexed fluorophosphine 325 described Phosphorus-carbon-aluminium cage structures have been isolated from the reactions of kinetically stable phospha-alkynes with trialkylaluminium compounds and new phosphaborane systems have been obtained from the reactions of phospha-alkynes with polyhedral boranes . Further studies of wo-phospha-alkyne coordination chemistry have appeared . The reactivity of the ion 326 has been explored. ... 

Dipoles generated from 3//-pyrido[l,2,3-rfe]quinoxalinium bromides react analogously with r-butyl phosphaethyne and yield regiospecifically phosphazaullacines of type (21) <94CCil2i>. 

Heating 1,2,4,5-tetrazine dicarboxylates (117) with /-butyl phosphaethyne yields a 1,2,3-azadiphospholyl-l,3-diphosphole (118 R = Me, Et) (Equation (27)) <88TL5867>. 

For several reasons the development of the chemistry of 6n heteroaromatic arsenic systems, for example arsinine (3), was much less vigorous than that of the phosphinines. While t-butylphos-phaethyne (4) and several other phosphaethynes are important building blocks for the synthesis of six-membered aromatic phosphorus heterocycles with more than one heteroatom, only one compound with a C=As triple bond, the 2,4,6-tri- -butylphenyl derivative (5), has been described <86AG(E)264>, and this has not been thoroughly studied. The only six-membered As-heteroaromatic system with more than one heteroatom is the l,3A -azarsinine (6) <88TL535>. Since pentavalent... 

Vibrational frequencies of the phosphaethyne cation were inferred from its X FI,... 

Rotational Spectra.—Phenyl, vinyl, ethynyl, and cyano phosphaethynes have been detected by microwave spectroscopy and their dipole moments and rotational constants calculated. ... 

Quite a few phosphaethynes have now been synthesised (Chapter 6.14). Unsymmetrically substituted derivatives do exist in syn and anti isomeric forms (13.81a) just as the longer-known ketox-imes (13.81b). 

Diphosphacyclobutene derivatives are synthesized from mesilylene-substituted phosphaethyne by treatment with i -BuLi (eq 44). The product 28 forms carbonyl complexes with transition metals such as chromium and tungsten. 

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