Insertion, Isomerization, and Cascade Reactivity of the Tethered Silylalkyl Uranium Metallocene (η⁵-C₅Me₄SiMe₂CH₂-κC)₂U

Abstract

Investigation of the insertion reactivity of the tethered silylalkyl complex (η(5)-C(5)Me(4)SiMe(2)CH(2)-κC)(2)U (1) has led to a series of new reactions for U-C bonds. Elemental sulfur reacts with 1 by inserting two sulfur atoms into each of the U-C bonds to form the bis(tethered alkyl disulfide) complex (η(5):η(2)-C(5)Me(4)SiMe(2)CH(2)S(2))(2)U (2). The bulky substrate N,N'-diisopropylcarbodiimide, (i)PrN═C═N(i)Pr, inserts into only one of the U-C bonds of 1 to produce the mixed-tether complex (η(5)-C(5)Me(4)SiMe(2)CH(2)-κC)U[η(5)-C(5)Me(4)SiMe(2)CH(2)C((i)PrN)(2)-κ(2)N,N'] (3). Carbon monoxide did not exclusively undergo a simple insertion into the U-C bond of 3 but instead formed {μ-[η(5)-C(5)Me(4)SiMe(2)CH(2)C(═N(i)Pr)O-κ(2)O,N]U[OC(C(5)Me(4)SiMe(2)CH(2))CN((i)Pr)-κ(2)O,N](2) (4) in a cascade of reactions that formally includes U-C bond cleavage, C-N bond cleavage of the amidinate ligand, alkyl or silyl migration, U-O, C-C, and C-N bond formations, and CO insertion. The reaction of 3 with isoelectronic tert-butyl isocyanide led to insertion of the substrate into the U-C bond, but with a rearrangement of the amidinate ligand binding mode from κ(2) to κ(1) to form [η(5):η(2)-C(5)Me(4)SiMe(2)CH(2)C(═N(t)Bu)]U[η(5)-C(5)Me(4)SiMe(2)CH(2)C(═N(i)Pr)N((i)Pr)-κN] (5). The product of double insertion of (t)BuN≡C into the U-C bonds of 1, namely [η(5):η(2)-C(5)Me(4)SiMe(2)CH(2)C(═N(t)Bu)](2)U (6), was found to undergo an unusual thermal rearrangement that formally involves C-H bond activation, C-C bond cleavage, and C-C bond coupling to form the first formimidoyl actinide complex, [η(5):η(5):η(3)-(t)BuNC(CH(2)SiMe(2)C(5)Me(4))(CHSiMe(2)C(5)Me(4))]U(η(2)-HC═N(t)Bu) (7).

Synthesis and Insertion Chemistry of Mixed Tether Uranium Metallocene Complexes

“…From this reaction mixture, a red‐brown crystalline material ( 7 ) can be obtained in a 48 % yield by cooling concentrated solutions of 7 in hexane. Analysis of the crystalline material by 1 H NMR spectroscopy showed a large number of resonances, possibly due to an asymmetric ligand environment,3b but the complexity of the spectrum made identification of the paramagnetic product very difficult, as discussed below.…”

“…As shown in Equation (4), exposure of 3 to 1 atm of CO produced solely [μ‐(η 5 ‐C 5 Me 4 SiMe 2 CH 2 C(N i Pr)O‐ κ 2 O , N )U(OC(C 5 Me 4 SiMe 2 CH 2 )CN( i Pr)‐ κ 2 O , N )] 2 ( 4 ) a product much more complicated than an enolate resulting from insertion and rearrangement as shown in Equation (2). Complex 4 apparently formed by a cascade of reactions, formally involving, not only CO insertion, but also UC bond cleavage, CN bond cleavage within the amidinate ligand, alkyl or silyl migration, and UO, CC, and CN bond formation 3b. This reaction demonstrates that tethered variations in the reactive metallocene wedge can lead to new types of transformations for metal–carbon bonds…”

“…Preliminary results have shown that the tethered complexes generated with 1 can provide structural information and reactivity not accessible with nontethered analogs 3b. By using CO as a reactivity probe, it was found that the tethered UC bonds react to form a crystallographically characterizable bis(tethered enolate) complex [(η 5 ‐C 5 Me 4 SiMe 2 C(CH 2 )O‐κ O ) 2 U] [ 2 ; Eq.…”

“…A much different reactivity pattern with the same (η 5 ‐C 5 Me 4 SiMe 2 CH 2 ‐κ C ) 2− ligand and CO was observed in the mixed tethered complex [(η 5 ‐C 5 Me 4 SiMe 2 CH 2 ‐κ C )U(η 5 ‐C 5 Me 4 SiMe 2 CH 2 C( i PrN) 2 ‐κ 2 N , N ′)] [ 3 ; Eq. (3)],3b formed by insertion of a single substrate into one of the UC bonds. As shown in Equation (4), exposure of 3 to 1 atm of CO produced solely [μ‐(η 5 ‐C 5 Me 4 SiMe 2 CH 2 C(N i Pr)O‐ κ 2 O , N )U(OC(C 5 Me 4 SiMe 2 CH 2 )CN( i Pr)‐ κ 2 O , N )] 2 ( 4 ) a product much more complicated than an enolate resulting from insertion and rearrangement as shown in Equation (2).…”

The actinides

“…DAB Me forms complexes [( Mes DAB Me ) 2 U(THF)] and [Cp 2 U( Mes DAB Me )].Indications are that the a-diimine ligands are present in the complexes as doubly reduced ene-diamides, and that the oxidation state of U is + 4 115. Sulfur inserts into U-C bonds affording [(Z 5 :Z 2 -C 5 Me 4 SiMe 2 CH 2 S 2 ) 2 U], but reaction with CO involves a complicated sequence of U-C bond cleavage, C-N bond cleavage of the amidinate ligand, alkyl or silyl migration, U-O, C-C, and C-N bond formations, and CO insertion affording eventually[(m-{Z 5 -C 5 Me 4 SiMe 2 CH 2 C(QN i Pr)O-k 2 O,N}U{OC(C 5 Me 4 SiMe 2 CH 2 )-CN( i Pr)-k 2 O,N}) 2 ] 116. Sulfur inserts into U-C bonds affording [(Z 5 :Z 2 -C 5 Me 4 SiMe 2 CH 2 S 2 ) 2 U], but reaction with CO involves a complicated sequence of U-C bond cleavage, C-N bond cleavage of the amidinate ligand, alkyl or silyl migration, U-O, C-C, and C-N bond formations, and CO insertion affording eventually[(m-{Z 5 -C 5 Me 4 SiMe 2 CH 2 C(QN i Pr)O-k 2 O,N}U{OC(C 5 Me 4 SiMe 2 CH 2 )-CN( i Pr)-k 2 O,N}) 2 ] 116.…”