One-Pot 1,1-Dihydrofluoroalkylation of Amines Using Sulfuryl Fluoride.

Sulfuryl fluoride, SO2F2, has been known and used as a fumigant for over 50 years but it has only recently gained widespread interest as a reagent for organic synthesis. Herein we report a novel application of sulfuryl fluoride gas in a new 1,1-dihydrofluoroalkylation reaction, which simply involves bubbling SO2F2 through a solution of amine, 1,1-dihydrofluoroalcohol, and diisopropylethylamine. The reaction is successful for a wide range of primary and secondary amines, as well as several 1,1-dihydrofluoroalcohols, to afford the 1,1-dihydrofluoroalkylated amines in 42% to 80% isolated yields. The reaction also displays excellent functional group tolerance. The ease of the one-pot activation and alkylation, combined with the wide substrate scope make this new procedure an attractive alternative to existing 1,1-dihydrofluoroalkylation methodologies.

Bimolecular Coupling as a Vector for Decomposition of Fast-Initiating Olefin Metathesis Catalysts.

The correlation between rapid initiation and rapid decomposition in olefin metathesis is probed for a series of fast-initiating, phosphine-free Ru catalysts: the Hoveyda catalyst HII, RuCl2(L)(═CHC6H4- o-O iPr); the Grela catalyst nG (a derivative of HII with a nitro group para to O iPr); the Piers catalyst PII, [RuCl2(L)(═CHPCy3)]OTf; the third-generation Grubbs catalyst GIII, RuCl2(L)(py)2(═CHPh); and dianiline catalyst DA, RuCl2(L)( o-dianiline)(═CHPh), in all of which L = H2IMes = N,N'-bis(mesityl)imidazolin-2-ylidene. Prior studies of ethylene metathesis have established that various Ru metathesis catalysts can decompose by ß-elimination of propene from the metallacyclobutane intermediate RuCl2(H2IMes)(κ2-C3H6), Ru-2. The present work demonstrates that in metathesis of terminal olefins, ß-elimination yields only ca. 25-40% propenes for HII, nG, PII, or DA, and none for GIII. The discrepancy is attributed to competing decomposition via bimolecular coupling of methylidene intermediate RuCl2(H2IMes)(═CH2), Ru-1. Direct evidence for methylidene coupling is presented, via the controlled decomposition of transiently stabilized adducts of Ru-1, RuCl2(H2IMes)Ln(═CH2) (Ln = py n'; n' = 1, 2, or o-dianiline). These adducts were synthesized by treating in situ-generated metallacyclobutane Ru-2 with pyridine or o-dianiline, and were isolated by precipitating at low temperature (-116 or -78 °C, respectively). On warming, both undergo methylidene coupling, liberating ethylene and forming RuCl2(H2IMes)Ln. A mechanism is proposed based on kinetic studies and molecular-level computational analysis. Bimolecular coupling emerges as an important contributor to the instability of Ru-1, and a potentially major pathway for decomposition of fast-initiating, phosphine-free metathesis catalysts.

Chelate-Assisted Ring-Closing Metathesis: A Strategy for Accelerating Macrocyclization at Ambient Temperatures.

Ring-closing metathesis (RCM) offers versatile catalytic routes to macrocycles, with applications ranging from perfumery to production of antiviral drugs. Unwanted oligomerization, however, is a long-standing challenge. Oligomers can be converted into the cyclic targets by catalysts that are sufficiently reactive to promote backbiting (e.g., Ru complexes of N-heterocyclic carbenes; NHCs), but catalyst decomposition limits yields and selectivity. Incorporation of a hemilabile o-dianiline (ODA) chelate into new catalysts of the form RuCl2(NHC)(ODA)(=CHPh) accelerates macrocyclization, particularly for dienes bearing polar sites capable of H-bonding: it may also inhibit catalyst decomposition during metathesis. Significant improvements relative to prior Ru-NHC catalysts result, with fast macrocyclization of conformationally flexible dienes at room temperature.

Olefin Metathesis at the Dawn of Implementation in Pharmaceutical and Specialty-Chemicals Manufacturing.

The recent uptake of molecular metathesis catalysts in specialty-chemicals and pharmaceutical manufacturing is reviewed.

Multinuclear Magnetic Resonance Investigation of Crystalline Alkali Molybdates.

A variety of crystalline alkali molybdate phases are characterized by (23)Na, (133)Cs, and (95)Mo magic-angle-spinning nuclear magnetic resonance (MAS NMR) to provide spectroscopic handles for studies of devitrification products in borosilicate nuclear waste glasses. The NMR parameters obtained from line-shape simulations are plotted as a function of various structural parameters to discern trends that may prove useful in the determination of unknown phases. These are applied to Cs3Na(MoO4)2, the most common precipitate found in cesium- and molybdenum-bearing model nuclear waste glasses, the crystal structure of which has not yet been determined, to provide structural constraints that may guide the refinement of powder X-ray diffraction data.

The divergent effects of strong NHC donation in catalysis.

Strong σ-donation from NHC ligands (NHC = N-heterocyclic carbene) is shown to have profoundly conflicting consequences for the reactivity of transition-metal catalysts. Such donation is regarded as central to high catalyst activity in many contexts, of which the second-generation Grubbs metathesis catalysts (RuCl2(NHC)(PCy3)([double bond, length as m-dash]CHPh), GII) offer an early, prominent example. Less widely recognized is the dramatically inhibiting impact of NHC ligation on initiation of GII, and on re-entry into the catalytic cycle from the resting-state methylidene species RuCl2(NHC)(PCy3)([double bond, length as m-dash]CH2), GIIm. Both GII and the methylidene complexes are activated by dissociation of PCy3. The impact of NHC donicity on the rate of PCy3 loss is explored in a comparison of s-GIIm, vs. u-GIIm, in which the NHC ligand is saturated H2IMes or unsaturated IMes, respectively. PCy3 loss is nearly an order of magnitude slower for the IMes derivative (a difference that is replicated, albeit smaller, for the benzylidene precatalysts GII). Proposed as an overlooked contributor to these rate differences is an increase in the Ru-PCy3 bond strength arising from π-back-donation onto the phosphine ligand. Strong σ-donation from the IMes ligand, coupled with the inability of this unsaturated NHC to participate in significant π-backbonding, amplifies Ru → PCy3 π-back-donation. The resulting increase in Ru-P bond strength greatly inhibits entry into the active cycle. For s-GII, in contrast, the greater π-acceptor capacity of the NHC ligand enables competing Ru → H2IMes back-donation (as confirmed by NOE experiments, which reveal restricted rotation about the Ru-NHC bond for H2IMes, but not IMes). Ru → PCy3 back-donation is thus attenuated in the H2IMes complexes, accounting for the greater lability of the PCy3 ligand in s-GIIm and s-GII. Similarly inhibited initiation is predicted for other metal-NHC catalysts in which a π-acceptor ligand L must be dissociated to permit substrate binding. Conversely, enhanced reactivity can be expected where such L ligands are pure σ-donors. These effects are expected to be particularly dramatic where the NHC ligand has minimal π-acceptor capacity (as in the unsaturated Arduengo carbenes), and in geometries that maximize NHC-M-L orbital interactions.

A reactive Ru-binaphtholate building block with self-tuning hapticity.

A versatile Ru-BINO building block is reported, which offers a straightforward entry point into the chemistry of atropisomeric binaphtholate complexes of ruthenium. Reaction of RuCl(2)(PPh(3))(3)6a with Tl(2)((S)-BINO) affords Ru((S)-BINO)(PPh(3))(2)7 as a mixture of isomers: in 7', the BINO ligand is bound via η(3)-CCO,η(1)-O' donors, and in symmetrical 7″, via η(3)-CCO,η(3)-O'C'C' interactions. The bis(enolate) BINO bonding mode in the latter, not previously observed for any metal, underscores the remarkable geometric and electronic flexibility of the binaphtholate moiety. The BINO ligand proves able to stabilize complexes containing as few as two, and as many as four, additional ligands in 7 and its derivatives, enabling a synthetic versatility that contrasts with that of the superficially similar o-catecholate complex Ru(o-cat)(PPh(3))(3). As with the important achiral Ru precursor 6a, complex 7 undergoes facile transformation into a range of products under mild conditions, including acetonitrile, pyridine, and vinylidene derivatives. Single-crystal X-ray structures are reported for three of these complexes: Ru(η(3),η(3)-(S)-BINO)(PPh(3))(2)7″, Ru(η(3),η(1)-(S)-BINO)(PPh(3))(2)(MeCN) 9, and Ru(η(3),η(1)-(S)-BINO)(PPh(3))(py)(2)11. (13)C{(1)H} NMR signatures are proposed for new and known BINO coordination modes (η(1)-O,η(1)-O'; η(1)-C1,η(1)-O'; η(3)-CCO,η(3)-O'C'C'; η(3)-CCO,η(1)-O'; η(6)-C(6),η(1)-O'), as a potential aid to further developments in late-metal BINO chemistry.