No abstract

The multinuclear complexes 1,3,5-[trans-I(Et3P)2PtC≡C]3C6H3 (1) and 1,2,4,5-[trans-I(Et3P)2PtC≡C]4C6H2 (2) were prepared via σ-acetylide synthetic methodologies by reaction of tri- and tetraethynylbenzene with diiodobis(triethylphosphine)platinum. The combination of this synthetic coupling strategy with the divergent synthetic principle for the formation of dendrimers led to organometallic first- and second-generation dendrimers with ethynylplatinum units in the main chain. The outer spheres of the dendrimers consist of either terminal acetylenic groups or bis(triethylphosphine)platinum iodide groups. All compounds were fully characterized by elemental analysis, mass spectrometry, NMR, and vibrational spectroscopy. The single-crystal structure of a first generation dendrimer 3 with terminal acetylene groups was determined by X-ray analysis. It shows an out-of-plane twisting of all three terminal 1,3,5-triethynylbenzene groups as well as a twisting of one of the coordination planes around a platinum atom, relative to the central aromatic ring.

Self-assembly reactions of hitherto unknown bis(4-pyridyl)silanes 2a,b with bis(triethylphosphine)platinum and bis(triethylphosphine)palladium bistriflates 5a,b lead to the formation of new silicon-containing rhomboids 6a−d. In addition, a similar carbon analogue 7 was prepared by reaction of bispyridyl acetal 4 and bis(triethylphosphine)platinum bistriflate (5a). Surprisingly, reaction of the bis(4-pyridyl)ketone (3) and the platinum complex 5a gave a similar rhomboid, 10, due to unexpected hydration of the ketone. The crystal structures of silicon complex 6a and its carbon analogue 7 were solved and compared to each other as well as to already known carbon-containing dinuclear rhomboids. In addition, the dinuclear bisporphyrin complex 8 was also characterized by X-ray structure analysis. Electrospray and FAB mass spectral data are reported as well, confirming the binuclear nature of the entities formed.

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.).

Dedicated to Professor Dieter Seebach on the occasion of his 60th birthday Cyclooligomerization reactions of phosphaalkynes in the coordination sphere of transition metals in which the metal complex fragment is incorporated in the product have played an important role in the development of phosphaalkyne chemistry.[1] Significant examples are the cyclodimerization of tert-butylphosphaacetylene (5a) to give the tricyclic zirconium complex 1, [2] cyclotrimerizations to give the vanadium and hafnium complexes 2[3] and 3, [4] and the formation of the zirconium and hafnium complexes 4[5] by cyclotetramerization. Treatment of 1, 3, and 4 with hexachloroethane leads to detachment of the metal complex fragments and formation of tBu-substituted 1,3,5,7-tetraphosphacubane (cyclodimerization of the residual molecule), [6] 1,3,5-triphosphabenzene (14a), [4] and 1,3,5,7-tetraphosphabarrelene. [5] Reactions of 2 with the same reagent have not yet been investigated. We now report on the chemoselective cyclooligomerization [7] of phosphaalkynes 5 a ± e with the vanadium(v) compounds tBuNVCl 3´D ME (6) [8] (DME 1,2-dimethoxyethane) and tBuNVCl 3 (13) [9] to produce the title compounds in good yields.Reaction of 5 a ± e with 6 in a molar ratio of 4:1 in toluene followed by column chromatography on alumina affords the previously unknown azatetraphosphaquadricyclanes 7 a ± e as yellow solids in yields of 47 ± 76 % (not optimized; Table 1).The elemental analyses and mass spectra (Table 2) indicate that the heteropolycyclic compounds are formed from four molecules of the phosphaalkyne 5 with loss of one molecule of an alkyne RCCR (see Scheme 1) and incorporation of the imide ligand from the vanadium compound 6.As an example the NMR data of 7 a are discussed here (for further spectroscopic data of the compounds 7, see Table 2).[ Table 2. Selected spectroscopic data for the azatetraphosphaquadricyclanes 7.[a]