Manganese(II) Alkyl/π-Allyl Complexes Resistant to Ligand Redistribution

The reaction of [Li­(THF)₄]­[(Mn­{C­(SiMe₃)₃})₃(μ-Cl)₄(THF)] (<b>1</b>) with K­(allyl^TMS2) (allyl^TMS2 = 1,3-C₃H₃(SiMe₃)₂) afforded [(η³-allyl^TMS2)­Mn­{C­(SiMe₃)₃}­{ClLi­(THF)₃}] (<b>2</b>). Attempted sublimation of <b>2</b> yielded [(η³-allyl^TMS2)­Mn­{C­(SiMe₃)₃}­(THF)] (<b>3</b>), indicating that <b>2</b> extrudes LiCl at elevated temperatures. Additionally, LiCl in <b>2</b> was displaced by reaction with PMe₃, quinuclidine, and dmap (dmap = 4-(dimethylamino)­pyridine), providing [(η³-allyl^TMS2)­Mn­{C­(SiMe₃)₃}­(L)] (L = PMe₃ (<b>4</b>), quinuclidine (<b>5</b>), dmap (<b>6</b>)). Treatment of PMe₃ complex <b>4</b> with BPh₃ yielded bright red [(allyl^TMS2)­Mn­{C­(SiMe₃)₃}] (<b>7</b>) accompanied by a precipitate of Ph₃B­(PMe₃). Mixed alkyl/π-allyl manganese­(II) complexes <b>2</b>–<b>7</b> are pyrophoric red solids with a high-spin d⁵ configuration, and all were crystallographically characterized. In the solid-state structures, the allyl ligands in <b>2</b>–<b>6</b> adopt a <i>syn</i>,<i>syn</i> configuration, whereas in base-free <b>7</b>, the allyl ligand has a <i>syn</i>,<i>anti</i> configuration. Complexes <b>4</b>, <b>5</b>, and <b>7</b> sublimed cleanly (5 mTorr) at 70, 90, and 50 °C, respectively. Complex <b>4</b> exhibited a particularly favorable combination of volatility and thermal stability, given that its appearance and powder X-ray diffraction pattern were unchanged after 24 h in a sealed flask at 100 °C. Compounds <b>2</b>–<b>7</b> are the first high-spin d⁵ mixed alkyl/allyl complexes, and <b>7</b> is the first room-temperature-stable example of a mononuclear transition-metal complex bearing only alkyl and allyl ligands

Base-Free and Bisphosphine Ligand Dialkylmanganese(II) Complexes as Precursors for Manganese Metal Deposition

The solid-state structures and the physical, solution magnetic, solid-state magnetic, and spectroscopic (NMR and UV/vis) properties of a range of oxygen- and nitrogen-free dialkylmanganese­(II) complexes are reported, and the solution reactivity of these complexes toward H₂ and ZnEt₂ is described. The compounds investigated are [{Mn­(μ-CH₂SiMe₃)₂}_∞] (<b>1</b>), [{Mn­(CH₂CMe₃)­(μ-CH₂CMe₃)₂}₂{Mn­(μ-CH₂CMe₃)₂Mn}] (<b>2</b>), [Mn­(CH₂SiMe₃)₂(dmpe)] (<b>3</b>; dmpe = 1,2-bis­(dimethylphosphino)­ethane), [{Mn­(CH₂CMe₃)₂(μ-dmpe)}₂] (<b>4</b>), [{Mn­(CH₂SiMe₃)­(μ-CH₂SiMe₃)}₂(μ-dmpe)] (<b>5</b>), [{Mn­(CH₂CMe₃)­(μ-CH₂CMe₃)}₂(μ-dmpe)] (<b>6</b>), [{Mn­(CH₂SiMe₃)­(μ-CH₂SiMe₃)}₂(μ-dmpm)] (<b>7</b>; dmpm = bis­(dimethylphosphino)­methane), and [{Mn­(CH₂CMe₃)­(μ-CH₂CMe₃)}₂(μ-dmpm)] (<b>8</b>). Syntheses for <b>1</b>–<b>4</b> have previously been reported, but the solid-state structures and most properties of <b>2</b>–<b>4</b> had not been described. Compounds <b>5</b> and <b>6</b>, with a 1:2 dmpe/Mn ratio, were prepared by reaction of <b>3</b> and <b>4</b> with base-free <b>1</b> and <b>2</b>, respectively. Compounds <b>7</b> and <b>8</b> were accessed by reaction of <b>1</b> and <b>2</b> with 0.5 equiv or more of dmpm per manganese atom. An X-ray structure of <b>2</b> revealed a tetrametallic structure with two terminal and six bridging alkyl groups. In the solid state, bisphosphine-coordinated <b>3</b>–<b>8</b> adopted three distinct structural types: (a) monometallic [LMnR₂], (b) dimetallic [R₂Mn­(μ-L)₂MnR₂], and (c) dimetallic [{RMn­(μ-R)}₂(μ-L)] (L = dmpe, dmpm). Compound <b>3</b> exhibited particularly desirable properties for an ALD or CVD precursor, melting at 62–63 °C, subliming at 60 °C (5 mTorr), and showing negligible decomposition after 24 h at 120 °C. Comparison of variable-temperature solution and solid-state magnetic data provided insight into the solution structures of <b>2</b>–<b>8</b>. Solution reactions of <b>1</b>-<b>8</b> with H₂ yielded manganese metal, demonstrating the thermodynamic feasibility of the key reaction steps required for manganese­(II) dialkyl complexes to serve, in combination with H₂, as precursors for metal ALD or pulsed CVD. In contrast, the solution reactions of <b>1</b>–<b>8</b> with ZnEt₂ yielded a zinc–manganese alloy with an approximate 1:1 Zn/Mn ratio

Overcoming a Tight Coil To Give a Random “Co” Polymer Derived from a Mixed Sandwich Cobaltocene

Reversible addition–fragmentation transfer (RAFT) polymerization of a η⁵-cyclopentadienylcobalt-η⁴-cyclobutadiene (CpCoCb) containing monomer under a wide variety of experimental conditions (e.g., different solvents, temperatures, RAFT agents, concentrations, and [RAFT agent]/[initiator]) was examined. In all cases the results revealed that although the monomer was being consumed over the course of the reaction, there was no significant increase in the molecular weight of the resulting polymer. It was determined that as the polymer chain grows (DP ≈ 10), a tight coil morphology was adopted, which hinders the approach of an additional, sterically demanding CpCoCb-containing monomer. This resulted in premature termination/chain transfer reactions rather than an increase in the polymer chain length. To address this problem, methyl acrylate (MA) with its lower steric demand was copolymerized with the bulky CpCoCb-containing monomer to act as a spacer. This provided the necessary steric relief and an opportunity for the metallopolymer to grow. This copolymerization resulted in dramatic improvements in the polydispersity and molecular weight of the end material. In subsequent experiments, the random copolymer was used as a macro-RAFT agent to prepare diblock copolymers, with good control over the molecular weight, allowing for an examination of the self-assembly behavior of the block copolymer in the solid state