Ethylene Oligomerization and Polymerization by Palladium(II) Methyl Complexes Supported by Phosphines Bearing a Perchlorinated 10-Vertex closo-Carborane Anion Substituent

Abstract

The synthesis and ethylene reactivity of the zwitterionic Pd methyl complexes (κ 2 -P,Cl-PR 2 CB 9 Cl 9 )PdMe-(THF) (7, R = i Pr; 8, R = Ph) and (κ 2 -P,O-P(o-OMe-Ph) 2 CB 9 Cl 9 )PdMe(THF) (9), which contain the first phosphines appended with anionic 10-vertex perchlorinated closo-carboranes, are described. Complexes 7 and 8 oligomerize ethylene (23 °C, 2 atm) to a Schulz−Flory distribution of C 4 −C 10 olefins with TOFs of ca. 8000 and 1800 t.o./h, respectively. 8 is ca. 4 times more active than the analogous (κ 2 -P,F-ortho-PPh 2 C 6 H 4 BF 3 )PdMe(L) (L = pyridine or collidine) system reported by Jordan and Piers, which produces butenes. Complex 9 reacts with ethylene to yield polyethylene wax (M n ca. 1000, Đ ca. 1.5) that is similar to commercial Fischer−Tropsch waxes. The activities of 7−9 are independent of ethylene pressure and the presence of B(C 6 F 5 ) 3 , suggesting that the catalyst resting state is the corresponding (PR 2 CB 9 Cl 9 )PdR(H 2 CCH 2 ) adduct. The molecular weights of the oligomer/polymer products are independent of ethylene pressure, which is consistent with an associative chain transfer mechanism. Reaction of 9 with ethylene generates the corresponding ethylene complex (κ 2 -P,O-P(o-OMe-Ph) 2 CB 9 Cl 9 )PdMe(H 2 CCH 2 ), which inserts ethylene at −20 °C with a barrier (ΔG ⧧ insertion ) of 18.1 kcal/mol.

Characterization of Reactive Organometallic Species via MicroED

“…Dimeric palladium(I) species featuring Pd–Pd bonds have been previously reported to react with a variety of small molecules to give homolytic cleavage 27 or insertion products. 28 Pd(I) dimer 2 (Figure 2), synthesized by thermolysis or UV irradiation of the methyl palladium phosphine precursor, 29 was fully characterized by single crystal XRD (Figure 2B) and multinuclear NMR (see Supporting Information). To study the reactivity of this species ( 2 ), a THF solution was treated with ethylene gas, which interestingly led to a dramatic color change and precipitation of a yellow solid (Figure 2A).…”

Characterization of reactive organometallic species via MicroED

“…Dimeric palladium(I) species featuring Pd-Pd bonds have been previously reported to react with a variety of small molecules to give homolytic cleavage 13 or insertion products. 14 Pd(I) dimer 2 (Figure 2), synthesized by thermolysis or UV irradiation of the methyl palladium phosphine precursor, 15 was fully characterized by single crystal XRD (Figure 2B) and multinuclear NMR (see supporting information). To study the reactivity of this species (2) a THF solution was treated with ethylene gas, which interestingly led to a dramatic color change and precipitation of a yellow solid (Figure 2A).…”

Strongly Coordinating Ligands To Form Weakly Coordinating Yet Functional Organometallic Anions

“…Over the last several years, our group has begun to investigate nonclassical applications of closo -carborane anions 1 (Figure ). , In one embodiment of this approach, we covalently attach the anions to ligand frameworks, such as phosphines − and N-heterocyclic carbenes (NHCs). − The carborane anions are used as bulky and charged alkyl or aryl surrogates, and we have demonstrated the utility of such ligands in catalysis. ,,− NHC 2 (Figure ) is technically a dianionic carbenoid because it, and related species, , have been isolated as alkali metal complexes. With respect to NHC 2 , we have reported only a single anionic Au­(I) compound 3 and disclosed no reactivity or further synthetic elaboration of this species (Figure ).…”