Challenges in Catalytic Hydrophosphination

Despite significant advances, metal-catalyzed hydrophosphination has ample room for discovery, growth, and development. Many of the key successes in metal-catalyzed hydrophosphination over the last decade have indicated what is needed and what is yet to come. Reactivity that is absent from the literature also speaks to the challenges in catalytic hydrophosphination. This Concept article discusses and highlights recent developments that address the ongoing challenges, and identifies areas in metal-catalyzed hydrophosphination that are underdeveloped. Advances in product selectivity, catalyst design, and both unsaturated and phosphine substrates illustrate the ongoing development of the field. Like all catalytic transformations, the benefits are realized through catalyst, ligand, and conditions, and consideration of those features are the route to a yet more efficient and broadly applicable reaction

Zirconium-catalyzed alkene hydrophosphination and dehydrocoupling with an air-stable, fluorescent primary phosphine

Zirconium-catalyzed alkene hydrophosphination and dehydrocoupling with an air-stable, fluorescent primary phosphine 8-[(4-phosphino)phenyl]-4,4-dimethyl-1,3,5,7-tetramethyl-2,6-diethyl- 4-bora-3a,4a-diaza-s-indacene furnishes fluorescent phosphine products. Hydrophosphination of the fluorescent phosphine produces products with a complete selectivity for the secondary product. A key intermediate in catalysis, a zirconium phosphido compound, was isolated

Zirconium-Catalyzed Intermolecular Double Hydrophosphination of Alkynes with a Primary Phosphine

Catalytic double hydrophosphination of internal alkynes and primary phosphines is possible using a zirconium complex, [κ⁵<i>-N,N,N,N,C</i>-(Me₃SiNCH₂CH₂)₂NCH₂CH₂NSiMe₂CH]Zr (<b>1</b>). The reaction proceeds via stepwise hydrophosphination to give vinyl phosphine products, which can be isolated or further converted to the respective 1,2-bis­(phosphino)­ethane (i.e., double hydrophosphination). The catalysis is highly selective for formation of secondary phosphine products

Intermolecular Zirconium-Catalyzed Hydrophosphination of Alkenes and Dienes with Primary Phosphines

Catalytic hydrophosphination of terminal alkenes and dienes with primary phosphines (RPH₂; R = Cy, Ph) under mild conditions has been demonstrated using a zirconium complex, [κ⁵-<i>N</i>,<i>N</i>,<i>N</i>,<i>N</i>,<i>C</i>-(Me₃SiN­CH₂CH₂)₂­NCH₂CH₂­NSiMe₂­CH]Zr (<b>1</b>). Exclusively anti-Markovnikov functionalized products were observed, and the catalysis is selective for either the secondary or tertiary phosphine (i.e., double hydrophosphination) products, depending on reaction conditions. The utility of the secondary phosphine products as substrates for further elaboration was demonstrated with a platinum-catalyzed asymmetric alkylation reaction

Visible Light Photocatalysis Using a Commercially Available Iron Compound

[CpFe­(CO)₂]₂ (<b>1</b>) (Cp = η⁵-C₅H₅) is an effective precatalyst for the hydrophosphination of alkenes with Ph₂PH under visible light irradiation, which appears to be a unique way to promote metal-catalyzed hydrophosphination. Additionally, <b>1</b> is a photocatalyst for the dehydrogenation of amine boranes and formation of siloxanes from tertiary silanes. These reactions have similar, if not improved, reactivity over the same transformations using <b>1</b> or related CpFeMe­(CO)₂ under UV irradiation, consistent with the notion that hydrophosphination with <b>1</b> proceeds via formation of CpFe­(CO)₂^•. These results demonstrate that catalyst selection can avail the use of commercially available LED bulbs as photon sources, potentially replacing mercury arc lamps or other energy intensive processes in known or new catalytic reactions

Light-Driven, Zirconium-Catalyzed Hydrophosphination with Primary Phosphines

Catalytic hydrophosphination using [κ⁵-<i>N,N,N,N,C</i>-(Me₃SiNCH₂CH₂)₂­NCH₂CH₂­NSiMe₂CH₂]Zr (<b>1</b>) under photolysis substantially enhances activity and avails greater substrate scope. Quantitative conversions of alkenes to secondary phosphines are reached in as little as 20 min at ambient temperature with <b>1</b> under ultraviolet or visible irradiation. A larger class of unactivated alkenes are now facile substrates under photolysis conditions, and <b>1</b> can engage in a previously unknown tandem inter/intramolecular hydrophosphination of 1,4-pentadiene to give the heterocyclic phosphorinane product. Computational and spectroscopic data indicate that photoexcitation of <b>1</b> at a variety of wavelengths results in P n → Zr d charge transfer. This excitation appears to accelerate catalysis by promoting substrate insertion at the Zr–P bond based on experimental observations

Ocean carbon cycling in the Indian Ocean: 2. Estimates of net community production

The spatiotemporal variability of ocean carbon cycling and air-sea CO2 exchange in the Indian Ocean was examined using inorganic carbon data collected as part of the World Ocean Circulation Experiment (WOCE) cruises in 1995. Several carbon mass balance approaches were used to estimate rates of net community production (NCP) in the Indian Ocean. Carbon transports into and out of the Indian Ocean were derived using mass transport estimates of Robbins and Toole (1997) and Schmitz (1996), and transoceanic hydrographic and TCO2 sections at 32°S and across the Indonesian Throughflow. The derived NCP rates of 749 ± 227 to 1572 ± 180 Tg C yr?1 (0.75–1.57 Pg C yr?1) estimated by carbon mass balance were similar to new production rates (1100–1800 Tg C yr?1) determined for the Indian Ocean by a variety of other methods (Louanchi and Najjar, 2000; Gnanadesikan et al., 2002). Changes in carbon inventories of the surface layer were also used to evaluate the spatiotemporal patterns of NCP. Significant NCP occurred in all regions during the Northeast Monsoon and Spring Intermonsoon periods. During the Southwest Monsoon and Fall Intermonsoon periods, the trophic status appears to shift from net autotrophy to net heterotrophy, particularly in the Arabian Sea, Bay of Bengal, and 10°N to 10°S zone