Dihydrogen and carbon dioxide react reversibly with the three-coordinate complex (EtsP)2PtGe-[N(SiMea)2]2• These reactions demonstrate the ability of germylenes to act as strong supporting ligands, while introducing new modes of reactivity via formal Ge(II) / Ge(IV) interconversion.Despite the synthesis of many types of germylenes and metal-germylene complexes, the observed reactiv-

The synthesis of three novel Pd germylene complexes is reported. (Ph3P)2PdGe[N(SiMe3)2]2 (1) was synthesized by ligand substitution of (Ph3P)4Pd, whereas (Et3P)PdGe[N(SiMe3)2]2 (2) and {dppePdGe[N(SiMe3)2]2}2 (3b) (dppe = (diphenylphosphino)ethane) were synthesized by photolytic reduction of their corresponding phosphine oxalato complexes followed by addition of the germylene ligand. In solution, 3b exists in equilibrium with the monomeric dppePdGe[N(SiMe3)2]2 (3a). The germylene ligand of 2 was found to be 1 order of magnitude more labile than the analogous Pt system and 2 orders of magnitude less labile than the analogous Ni system. The reactivity of these new palladium germylenes toward O2 is described.

The reaction of (Et(3)P)(2)PtGe[N(SiMe(3))(2)](2) with dioxygen yields (Et(3)P)(2)Pt(&mgr;-eta(2)-O(2))Ge[N(SiMe(3))(2)](2) (1). Exposure of 1 to light resulted in a rearrangement to (Et(3)P)(2)PtO(2)Ge[N(SiMe(3))(2)](2) (2a), the first example of a bidentate, dianionic germanate ligand. The isomerization was judged to occur via an intramolecular O-O bond scission and rotation of the Pt-Ge bond. No free germylene was detected, and the reaction was found to be zero order. An analogue of 2a was prepared by direct reaction of (Ph(3)P)(2)PtO(2) with Ge[N(SiMe(3))(2)](2) yielding (Ph(3)P)(2)PtO(2)Ge[N(SiMe(3))(2)](2) (2b). Addition of SO(2) to 1 results in the formation of the bridging sulfate (Et(3)P)(2)Pt(&mgr;-eta(2)-SO(4))Ge[N(SiMe(3))(2)](2) (3). An infrared spectroscopy study of the sulfate reaction was performed using oxygen-18. The results indicate that direct insertion of SO(2) into the O-O bond does not occur. Formaldehyde was also observed to insert into the Pt-O bond of 1 giving (Et(3)P)(2)Pt(&mgr;-eta(2)-OCH(2)OO)Ge[N(SiMe(3))(2)](2) (5).

The reaction of (Et 3 P) 2 PtGe[N(SiMe 3 ) 2 ] 2 (1) with nitrosobenzene and 2-nitrosotoluene yields (Et 3 P) 2 -PtN(Ph)OGe[N(SiMe 3 ) 2 ] 2 (3a) and (Et 3 P) 2 PtN(o-Tol)OGe[N(SiMe 3 ) 2 ] 2 (3b), respectively. The reactivity of 3a with SO 2 , H 2 CO, CO 2 , and PhNCO was explored yielding the five-membered heterocyclic complex (Et 3 P) 2 -PtS(O) 2 N(Ph)OGe[N(SiMe 3 ) 2 ] 2 (6a) and the six-membered heterocyclic complexes (Et 3 P) 2 PtOC (H) respectively. The structures of 3a, 6a, 7a, and 9a were determined by single-crystal X-ray diffraction. 3b was observed to react in a fashion similar to 3a as demonstrated by reactions with SO 2 and H 2 CO which gave (Et 3 P) 2 PtS(O) 2 N(o-Tol)OGe[N(SiMe 3 ) 2 ] 2 (6b) and (Et 3 P) 2 PtOC(H) 2 N(o-Tol)OGe[N(SiMe 3 ) 2 ] 2 (7b). Complexes 6a and 6b represent the first isolated and characterized examples of metal-stabilized -S(O) 2 N-(R)O-fragments, the isoelectronic analogue of an elusive intermediate proposed as the first step in ContactProcess for the oxidation of SO 2 by platinum catalysts. As a group, the reactions in this paper demonstrate the cooperative ability of metal-germylenes to activate unsaturated organic substrates and promote their subsequent chemical modification, while avoiding scission of the Pt-Ge bond.

A 1 M solution of ti-iisobutylaluminum in toluene ( I 8 inL. 1 8 mmol) was added to I (700 mg, 0.45 nimol) in freshly distilled. dry tolucne (15 ml) at 0 -C The reaction iiiixture war then stirred at 40 C for 6 h. After coinpletion of the reaction. exces? triisobutylnluininiim was quenched with ice-cold water The reaction mixture was filtered. and the organic phase separated. The water layer u'as extracted twice with ethyl acetate The combined organic fractions were dried (MgSO,) and concentrated. and the residue subjected to flash chromatography (eluent. cyclohexanr ethyl acetate 2,'l) to givc 2 as a syrup(158 mg. 79%)Received: Scptcinber 23 l W 6 [Z95851E] Ciei-man version A n p i i ' . ( ' h o i i . 1997. 109. 513-516

Group 10 metal germylene complexes of general formula (R 3 P) 2 MGeQ 2 are found to be highly photosensitive. Ambient fluoresent lighting causes complete decomposition of nickel germylene species in less than one minute in the presence of germylene traps. The formation of metallacycle (Et 3 P) 2 Pt(µ-η 2 -H 2 CO)Ge[N-(SiMe 3 ) 2 ] 2 and the photochemical cycloreversion reaction are also reported.

The use of a new electron‐withdrawing germane, H2Ge[3,5‐(CF3)2C6H3]2 (3), has facilitated the isolation and characterization of three new complexes implicated in the dehydrogenative coupling of bisarylgermanes by Pt0‐phos‐phane complexes. The intermediates include a digermyl species, trans‐[(Et3P)2Pt{GeH(Ar)2}2] (7), a bound digermane showing the first stage of Ge‐Ge catenation, cis‐[(Et3P)2Pt(H){Ge(Ar)2‐GeH(Ar)2}] (8), and the Ge‐H activated form of this product, [(Et3P)2HPtGe(Ar)2‐Ge(Ar)2PtH(PEt3)2] (6). Complexes such as 6 and 8 have not previously been isolated as intermediates in dehydrogenative coupling reactions. An X‐ray crystal structure was determined for complex 6, confirming the cis geometry of the hydrogen and germanium ligands; this provides yet another example of the stability of germyl hydrides towards reductive elimination. A similar cis geometry was observed for complex 8. Performing the dehydrogenative coupling reaction under a CO2 atmosphere failed to yield any products containing trapped germylene species.

Germanium dioxide in the presence of 5% KOH reacted with dimethyl carbonate (DMC) at 250 degrees C to give (MeO)(4)Ge. The reaction of GeO(2) and DMC is similar to that reported for SiO(2); however, the rate of reaction for germanium is much higher than that of the corresponding silicon reaction. In a side-by-side experiment using SiO(2) and GeO(2) where the surface area of the silicon dioxide was 2 orders of magnitude higher than that of the GeO(2), the base-catalyzed reaction with DMC was about an order of magnitude higher for the germanium dioxide. When GeO(2) and 5% KOH were reacted with DMC at 350 degrees C, two products formed: (MeO)(4)Ge (70%) and MeGe(OMe)(3) (30%). Confirmation of the identity of MeGe(OMe)(3) was by GCMS, (1)H and (13)C NMR, and comparison to an authentic sample made by reaction of MeGeCl(3) with NaOMe. Experiments to determine the mechanism of the direct formation of Ge-C from GeO(2) ruled out participation from CO, H(2), or carbon. The KOH-catalyzed reaction of other metal oxides was explored including B(2)O(3), Ga(2)O(3), TiO(2), Sb(2)O(3), SnO(2), and SnO. Boron reacted to give unknown volatile products. Antimony reacted to give a solid which analyzed as Sb(OMe)(3). SnO reacted with DMC to give a mixture that included (MeO)(4)Sn and possibly Me(3)Sn(OMe).