Platinum-Catalyzed Bis-Germylation of Alkynes with Organodigermanes and Cyclic Oligogermanes

Abstract

Hexamethyldigermane, Me3GeGeMe3, reacted with various alkynes in the presence of platinum complexes at 120 °C to afford Z–1,2-bis(germyl)ethenes in moderate to good yields. Terminal alkynes exhibit higher reactivities than internal ones. [Pt(acac)2] and [Pt(dba)2] serve as efficient catalysts, while [Pt(PPh3)4], [PtCl2(PPh3)2], and [Pt(dba)2]-phosphite were found to be inactive. Four- and six-membered cyclic oligogermanes, such as dodecamethylcyclohexagermane, (Me2Ge)6, reacted with alkynes in the presence of platinum catalysts to yield 1,4-digermacyclohexa-2,5-dienes in ca. 30% yield. The reactions of phenylacetylene with 1,2-digermacyclohexa-3,5-dienes afforded the corresponding 1,4-digermacycloocta-2,5,7-trienes in 93% yield. Bis(germyl)platinum complexes having various tertiary phosphine ligands have been prepared as models of a key intermediate in the above mentioned catalytic bis-germylation of alkynes, and their structures have been established by spectroscopic methods and X-ray crystallography. Bis(germyl)platinum complexes reacted with phenylacetylene to give the corresponding insertion products, germyl(germylvinyl)platinum species, whose structures have been determined by spectroscopic and X-ray analysis. Germyl(germylvinyl)platinum complexes were found to liberate a bis-germylation product of the alkyne upon heating. The result supports a mechanism involving the oxidative addition of a digermane to a Pt(0) complex, the insertion of an alkyne into one of the two Pt-Ge bonds to give a germyl(germylvinyl)platinum species, and the reductive elimination of the bis-germylation product of the alkyne. Evidence suggesting the extrusion of a germylene unit from the bis-germylplatinum species has been obtained, accounting for the generation courses of other by-products.

Preparation, structural characterization of 1,2-digermacyclobut-3-enes, and their palladium-catalyzed insertion of alkynes

“…Then, Z-a,bbis(chlorodiethylgermyl)styrene (1b) was purified simply by distillation (Kugelrohr) under reduced pressure to give 1b (7.71 g, 0.20 mol, 43%). 1b: bp 80-140°C/0.02 mmHg; 1 H NMR (d, CDCl 3 ) 1.09 (m, 10H, EtGe), 1.25 (m, 10H, EtGe), 6.90 (s, 1H, CH@), 7.10-7.42 (m, 5H, phenyl ring protons); 13 C NMR (d,CDCl 3 ) 8.19,8.72,12.99,15.94,126.06,127.36,128.55,144.62,148.15,158.84. MS m/z (relative intensity): 405 (88), 370 (11), 341 (10), 268 (33), 239 (30), 166 (100).…”

“…Za,b-bis(chlorodiisopropylgermyl)styrene (1c) was purified simply by distillation (Kugelrohr) under reduced pressure in 1. Hz, 2H, CH), 6.89 (s,1H,CH@),5H,Ph); 13 C NMR (d,CDCl 3 ) 18.36,18.72,19.20,19.53,21.62,24.69,126.35,127.31,128.51,145.52,149.68,158.05. MS m/z (relative intensity): 490 (M + , 13), 447 (100), 404 (26).…”

“…Under these conditions, 2b was stable for one month. 2b: 1 H NMR (d,20H,EtGe),5H,Ph),7.69 (s,1H,CH@); 13 C NMR (d,CDCl 3 ) 8.85,9.55,10.70,10.90,126.52,127.74,128.53,140.88,149.72,161.74. MS m/z (relative intensity): 364 (M + , 41), 349 (46), 335 (27), 320 (8), 262 (100), 233 (47), 204 (24), 175 (31), 160 (49).…”

“…1,1,3, was obtained as by-product by chromatography with a short column packed with silica-gel eluted with diethylether and Kugelrohr-distilled (84-95°C/0.085 mmHg) in 6.8% yield (450 mg, 1.19 mmol). 3b: 1 H NMR (d,20H,EtGe),7.24 (s,1H,CH@),5H,phenyl); MS m/z (relative intensity): 380 (M + , 18), 351 (100), 322 (53).…”

Ring Flipping of Seven-membered and Eight-membered Dithienodisila-heterocycles

“…The conformational energy barrier for the ring inversion of 1,3,6-cyclooctatriene was calculated to be only 4.1 kcal/mol above the ground state. On the other hand, the 1 H and 13 C NMR spectra of the eight-membered disilacarbocycles, 1,1,4,4-tetramethyl-5,6, 7,8-tetraphenyl-1,4-disilacycloocta-2,5,7-triene derivatives 2,3 having phenyl substituents on the ring and 1,1,6,6-tetramethyl-1,6-dihydrotribenzo-[b,e,g][1,4]-disilocine 4 having a biarylene moiety such as a biphenylene, indicated that the two methyl groups on the silicon atom of these eightmembered disilacarbocycles were nonequivalent. This nonequivalence of the two methyl groups on the silicon atom in the compounds may be due to the steric repulsions between the methyl substituents on the silicon atom and the phenyl substitutents or biphenylene moiety of the eight-membered ring.…”