Methanide Complexes of s-Block and Rare Earth Metals

Chapters 2-3 focus on the proligand tris(2-pyridylthio)methane (HTptm, HC(S–C5H4N)3) and novel complexes obtained from reactivity with alkaline earth (Ae) reagents: 1) Grignard reagents (2.1-X, X = Cl, Br, I); 2) dialkylmagnesium reagents (3.1 and 3.2); 3) Ae bis-amides (3.3-Ae, Ae = Mg-Ba). Tptm underwent a facile C–S bond activation process with the more reactive co-ligands (alkyl or amido), which was studied via DFT and NMR studies. These showed a non-linear decomposition involving the novel transfer of an alkyl group onto the methanide carbon. 3.3-Mg and 3.3-Ca were also tested as hydrophosphination catalysts for selected alkenes and alkynes, including the first example of mono-hydrophosphination of 4-ethynylpyridine, achieved with high conversions and excellent regio- and stereochemical control.

Chapters 4-5 covers the pursuit of Ae and divalent lanthanide alkylidenes, starting from the iminophosphoranomethanide (RNPC-H, {CH(R)P(Ph)2=NSiMe3}–, R = SiMe3, SitBuMe2). Group 1 (Li–K) salts and relative crown ether adducts of [A(TMSNPC-H)]2 (4.3-A, A = Li–K) were prepared and fully characterized. The use of 12-crown-4 and 15- crown-5 with 4.3-Li and 4.3-Na respectively yielded the rare ‘ate’ complexes [A(crown)2]+[A(TMSNPC-H)2]–. 4.3-K was also used to prepare [M(TMSNPC-H)2(THF)x] (5.1-M, M = Mg-Ba, Eu, Yb) and [RE(TMSNPC-H)3] (5.2-M; RE = Y, La, Pr, Sm). NMR analysis revealed underlying changes in the M–C bond character and intraligand bonding, corroborated by XRD and DFT. The 171Yb{1H} NMR of 5.1-Yb was recorded (δ = 1109 ppm), representing the first ytterbium NMR of a compound of this type.

Chapter 6 focuses on a DFT study of NPC ligand system and target alkylidenes, [M(TMSNPC)(TMSNPC-H)]– (6.2-M, M = Mg-Ba, Eu, Yb) and [M(TMSNPC)2]2– (6.3-M, M = Mg-Ba, Eu, Yb). This study shows that the proposed species feature σ-bonds possessing some degree of covalency (M = Mg–Ba, Eu), and completely ionic π- interactions with the exception of 6.2-Yb and 6.3-Yb.