Selective Syntheses of 1,3‐Diphosphacyclobutadiene, Dewar‐1,3,5‐triphosphabenzene, 1,3,5‐Triphosphabenzene, and 1,3,5,7‐Tetraphosphabarrelene by Cyclooligomerization of Phosphaalkynes

Abstract

Dcdic,uted to ProfiJssor MorIjrcd Regit: on ihi, o i n r s i o t i qf'kis 60th birtlidu,rThe rcccntly described synthesis of the 1,3.5,7-tetraphosphabarrelene complex 3 from rerr-butylphosphaacetylene 1 and bis-(cyc1ooctatetraene)zirconium [Zr(~ot),]"~ led to the assumption that the 12-valence electron fragment [cotM], formed as an intermediate by elimination of one of the two cot ligands, is an ideal tetnplatc for cyclooligomerizations of phosphaalkynes. Phosphaalkynes are known to cyclodimerize on the 14-valence electron fragments [Cp,M'] (M = Zr, Hf) to give the 1,3diphosphabicyclo[l .l .O]butanediyl metallocenes such as 2.l" for a further 0.5 h at about 140 C and then the solvent was removed at 0.5 mhar. The resulting brown solid was suspended in pentane (20 mL). filtered with a D3 frit. uashcd with pentme. and dricd at mhar. Recrystallization from tolucne afforded 6 a (1.83 g. 6 8 % ) as brown microcrystals: m.p. 163°C (decomp.). 8a: l(3.4 g, 34 mmol) was added dropwise to a solution of 5 a (4.0 g. 11.2 mmol) in toluene (1 0 mL) and pentane (10 mL) at -78 'T and stirred for 18 h at -78 C. The green-bro*n suspension was filtered at -78 C and the residue \lashed twice with pentaiie (2 x 20 mL). Recrystallization from THF (10 mL) aFforded 8 a (5.39 g.8 3 % ) as green inicrocr)stals: m.p. ca. 138 C (dccomp.). 9 h . I (1.3 g. 13 mmol) was added dropwisc to a solution of 5b (2 08 8.4.32 inmol) in Et,O (30 mLj at 0 ' C . After 1 h the reaction solution was cooled to -~3 0 C, the green crystals o f 9 h which precipitated &'ere filtered off and dried at l o -" mhiir; 9 b(2.8 g. X9%j; n1.p. 107 C (decomp.).13: Hexachloroethane (0.2 g, 0.X6 mmol) was added to a suspension of X a (0.5 g.0.86 mmol) in toluene (30 mL) at -~ 78 C. The reaction mixture was allowed to warm to room temperature over the course of 12 h. tiltci-ed. and the tiltrate was evaporated to dryness at 0.5 mhar. The residue has dissolved in pentme (20 m L ) nnd small amounts of insoluble material were removed by liltration. The yellow filtrate wiis concentrated to 5 mL and cooled t o -78 C. After 8 h. 0.14g of 13 (53%) had precipitated in the form of ii ycllow solid; m.p. X8 C (decomp.). 14. Hcxachloroethane (425 mg. 1.8 mmolj was added to a solution of 9b (1 3 g, 1.8 mmol) in toluene (10 mL) ;it room temperature end the mixture was stirred l'or 2 h. The solvent was removed at 0.5 mbar. the residue was taken up in pentnnc (40 mL) and filtered over Cclite to remove insoluhle material On cooling to -30 C small amounts of [his(triniethylsilyl)eyclooet~tetracne]h~ifniuin dichloride precipitated. which w a s likewise filtered off. The clear filtrutc was concentrated t o 20 mL. and subsequent cooling to -30 C led to the precipitation ol' 14 (3x0 nig. 70%) in the form of orange microcrystnls: m.p. about 128 C (decomp.).

Phospha‐Organic Chemistry: Panorama and Perspectives

“…[243] This experimental picture is rather surprising in the light of recent theoretical studies which indicate that all of the diphosphinine isomers show extensive cyclic delocalization, with the lowest energy form being the unknown 1,2-diphosphinine. [244,245] The much-sought-after 1,3,5-triphosphinine was first prepared by Binger et al [246] The best method for its preparation relies on the trimerization of phosphaalkynes in the presence of a vanadium(v) imido complex [see Eq. (48)].…”

Facile, Novel Methodology for the Synthesis of Spiro[pyrrolidin-3,3′-oxindoles]: Catalyzed Ring Expansion Reactions of Cyclopropanes by Aldimines

“…Recently, we have shown that synthetic dinuclear and trinuclear [7] metallophosphodiesterases based on calix [4]arenes [8] exhibit a very high catalytic activity in the transesterification of the RNA model substrate 2-hydroxypropyl-p-nitrophenyl phosphate (HPNP). [6,9,10] Here we report that 1-Zn 3 efficiently catalyzes the cleavage of RNA dinucleotides (3',5'-NpN) by the cooperative action of the Zn II centers, with high rate enhancement and significant nucleobase specificity. The heterotrinuclear complex 1-Zn 2 Cu is even more active; it mimics phosphodiesterases with a heterotrinuclear metal cluster including a Zn II center in the active site.…”

“…The apparent pK a of a Zn II -bound water molecule in 3-Zn is 7.9; [9] the value is lower for 1-Zn 3 due to hydrophobic and cooperative effects. [9,10] Therefore, it is likely that at pH 8 one or two Zn II centers in 1-Zn 3 are coordinated by a hydroxide ion. Furthermore, the activity reaches a Supporting information for this article is available on the WWW under http://www.wiley-vch.de/home/angewandte/ or from the author.…”

“…[9] The dissonant chargeaffinity pattern of cyclopropanes is manifest in their wellknown reactivity, when substituted with electron-withdrawing groups, to serve as homo-Michael acceptors. [10] Pioneering work by Danishefsky et al had established the participation of doubly activated cyclopropanes in tandem reactions resulting in ring formation. [11] By contrast, the strategy depicted in Scheme 1 necessitates nucleophilic ring opening of a singly activated ring system by a weakly nucleophilic aldimine.…”

Isolation of a Kinetically Stabilized 1,3,6-Triphosphafulvene

“…In 1995, 2,4,6-tri-tert-butyl-1,3,5-triphosphabenzene (1) was first reported, prepared through the trimerization of tert-butylphosphaacetylene (or 3,3-dimethyl-1-phospha-1-butyne), together with its valence isomer 2; [1] the structure of 1 was established in 1998. [2,3] Oligomerization of tert-butylphosphaacetylene has been utilized for the construction of various types of five-membered heterocyclic systems containing polycyclic systems.…”