Metal reduction with sodium naphthalenide

The insertion of a tin atom into a nonicosahedral carborane framework was first reported by Grimes and co-workers (233), following approaches similar to those which had previously been successful with transition metal reagents. Reduction of c/oso-2,4-C2B5H7 with sodium naphthalenide generates the C2B5H7 dianion, which on treatment with tin dichloride yields... 

Examples of derivatives of zerovalent niobium and tantalum are very rare. Cocondensation of vapors of the metals, generated by an electron gun furnace at 3000 °C, operating at a positive potential with dmpe, gave excellent yields (>60%) of stable crystalline [M(dmpe)3], which displays a distorted octahedral geometry. Attempts to obtain the corresponding niobium compound by reduction of NbCls with sodium naphthalenide at room temperature in the presence of an excess of dmpe failed and led to metal deposition. By contrast, reduction of MX5 by sodium amalgam in the presence of bipy or o-phen (LL) afforded the paramagnetic M(LL)3 adducts in ca. 80% yield. ... 

Significantly fewer unsupported and structurally characterized alkali metal-TM complexes are known, though they show similar motifs compared with their main group counterparts. For example, the cuprate complex [(THF)2Na-Cu(SFBu3)2j, 7, exhibits an almost linear Si—Cu—Si fragment (175.26(5)°) and a Na-Cu bond of 2.7393(18) A [68]. The rare 2,2 -biphosphinine-coordinated Ru complex 8 has been obtained from reduction of the corresponding Ru" chloride complex with sodium naphthalenide in DME. This has a Ru-Na bond of 3.072(2) A in the solid state [69] and is effective in salt metathesis reactions with Mel or RjSnCl (R = Me, Ph) to give substituted Ru" complexes. 

The dropwise addition of sodium naphthalenide to THF containing vanadium trichloride and l,2-bis(dimethylphosphino)ethane (dmpe) causes changes of colours suggesting a stepwise reduction from +2 to 0. Brown [V(dmpe)3] was isolated41 (fieff = 2.10BM) and IR data suggest octahedral coordination. The same complex was synthesized by a metal vapour technique.42 The ESR was that expected and the unit cell is cubic with a = 11.041(3) A. 

Of the homoleptic carbonylmetallates(l -) we have attempted to reduce, [Co(CO)4] appears to be the most difficult. Although the sodium salts of [M(CO)6] (M = V, Nb, and Ta) were quickly reduced in liquid ammonia by sodium metal to provide the corresponding trianions, [M(CO)5]3 (vide supra), it seems unlikely that we have ever effected complete reduction of Na[Co(CO)4] to Na3[Co(CO)3]. Even after 2 days of refluxing (at — 33°C) anhydrous ammonia solutions of Na[Co(CO)4] with excess Na, considerable amounts of the tetracarbonylcobaltate(l —) remained. Low yields of a heterogeneous-appearing brown to olive-brown insoluble solid were isolated this solid has been shown to contain Na3[Co(CO)3] (vide infra). As in the case of [Re(CO)s], we found that solutions of potassium in liquid ammonia were far more effective at reducing [Co(CO)4]-. However, unlike [Re(CO)s], [Rh(CO)4], or [Ir(CO)4] (vide infra), there was no evidence that [Co(CO)4] was reduced by sodium or potassium metal in hexa-methylphosphoric triamide. We observed that excess sodium naphthalenide slowly (over a period of 40-50 hr at room temperature) converted Na[Co(CO)4] in THF to an impure and insoluble brown powder that contained Na3[Co(CO)3], but this synthesis appeared to be of little or no utility. 

In 1973, the direct potassium metal reduction of zinc salts was reported.3 This active zinc powder reacted with alkyl and aryl bromides to form the alkyl- and arylzinc bromides under mild conditions.4 The reduction of anhydrous zinc salts by alkali metals can be facilitated through the use of electron carriers. Lithium and sodium naphthalenide reduce zinc salts to give highly reactive metal powders under milder and safer conditions. Graphite5 and liquid ammonia6 have also been employed as electron carriers in producing zinc powders. A highly dispersed reactive zinc powder was formed from the sodium metal reduction of zinc salts on titanium dioxide.7... 

These systems are not catalytic in the true sense because solvolysis, with resultant destruction of the active species, is needed to liberate NH3. However, by controlled solvolysis followed by removal of the NH3, a further cycle of reduction, N2 absorption, and solvolysis often can be made. Titanium retains activity through about five such cycles in the tetra-isopropoxytitanium-sodium-naphthalenide system in ether using propan-2-ol for solvolysis (10). By using a nonprotic Lewis acid, aluminum tribromide, the catalytic effect of Ti is demonstrated. When N2 (100 atm pressure) is treated with a mixture of titanium tetrachloride, metallic aluminum, and aluminum tribromide at 130°C as much as 284 mol of NH3 per mol of TiCl4 is obtained after hydrolysis. This, then, is a system for the catalytic nitriding of Al (13). A similar system operating electrochemically yields 6.1 mol NH3 per g atom Ti in 11 days (14). 

Molecule 1, CsHg The conceptual construction of the series 1-7 begins with a look at the known 1, bicyclo[l.l.l]pentane (Fig. 13.1). This is now a well-known compound, with ca. 150 references in Chemical Abstracts as of early 2007. The first preparation was reported in 1964 by Wiberg and Conner [5, 6], who made it in low yield by reducing l-bromo-3-bromomethylcyclobutane with metals or sodium naphthalenide electrochemical reduction proved better although the yield was still... 

Reaction of dichloro(pentamethylcyclopentadienyl)silane with lithium, sodium or potassium naphthalenide gives a mixture of elemental silicon, the corresponding alkali metal pentamethylcyclopentadienide and decamethylsilicocene (82) (equation 64)181. Compound 82 is formed as the only product in the reduction of dibromo-bis(pentamethylcyclopentadienyl)silane with potassium anthracenide (equation 65)182. 

From the experimental point of view, reductive desulfonylations with alkali metal arene radical anion complexes require a large excess of the radical anion, very short reaction times at low temperatures, and must be run under an inert atmosphere. Sodium or lithium naphthalenides in tetrahydrofuran at —78° or lower temperatures are typical reaction conditions. Tetrahydrofuran solutions of lithium naphthalenide are dark green. This color is lost when the substrate is added and restored once the reaction is finished. Upon completion, the excess reagent is quenched with a saturated aqueous solution of ammonium chloride or low molecular alcohols such as methanol or ethanol. 

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