Lanthanide N,N-Dimethylaminodiboranates as a New Class of Highly Volatile Chemical Vapor Deposition Precursors
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New lanthanide N,N-dimethylaminodiboranate (DMADB) complexes of stoichiometry Ln(H3BNMe2BH3)3 and Ln(H3BNMe2BH3)3(thf) have been prepared, where Ln = yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, and lutetium, except that isolation of the desolvated complexes proved difficult for Eu and Yb. The tetrahydrofuran (thf) complexes are all monomeric, and most of them adopt 13-coordinate structures in which each DMADB group chelates to the metal center by means of four B–H···Ln bridges (each BH3 group is κ2H; i.e., forms two B–H···Ln interactions). For the smallest three lanthanides, Tm, Yb, and Lu, the metal center is 12 coordinate because one of the DMADB groups chelates to the metal center by means of only three B–H···Ln bridges. The structures of the base-free Ln(H3BNMe2BH3)3 complexes are highly dependent on the size of the lanthanide ions: as the ionic radius decreases, the coordination number decreases from 14 (Pr) to 13 (Sm) to 12 (Dy, Y, Er). The 14-coordinate complexes are polymeric: each metal center is bound to two chelating DMADB ligands and to two “ends” of two ligands that bridge in a Ln(κ3H-H3BNMe2BH3-κ3H)Ln fashion. In the 13-coordinate complexes, all three DMADB ligands are chelating, but the metal atom is also coordinated to one hydrogen atom from an adjacent molecule. The 12-coordinate complexes adopt a dinuclear structure in which each metal center is bound to two chelating DMADB ligands and to two ends of two ligands that bridge in a Ln(κ2H-H3BNMe2BH3-κ2H)Ln fashion. The complexes react with water, and the partial hydrolysis product [La(H3BNMe2BH3)2(OH)]4 adopts a structure in which the lanthanum and oxygen atoms form a distorted cube; each lanthanum atom is connected to three bridging hydroxyl groups and to two chelating DMADB ligands. One B–H bond of each chelating DMADB ligand forms a bridge to an adjacent metal center. Field ionization MS data, melting and decomposition points, thermogravimetric data, and NMR data, including an analysis of the paramagnetic lanthanide induced shifts (LIS), are reported for all of the complexes. The Ln(H3BNMe2BH3)3 compounds, which are highly volatile and sublime at temperatures as low as 65 °C in vacuum, are suitable for use as chemical vapor deposition (CVD) and atomic layer deposition (ALD) precursors to thin films.
已合成化学计量比为Ln(H₃BNMe₂BH₃)₃和Ln(H₃BNMe₂BH₃)₃(thf)的镧系元素N,N-二甲基氨基二硼酸盐（N,N-dimethylaminodiboranate, DMADB）配合物，其中Ln涵盖钇、镧、铈、镨、钕、钐、钆、铽、镝、钬、铒、铥以及镥；但铕（Eu）和镱（Yb）的去溶剂化配合物难以分离得到。该类四氢呋喃（tetrahydrofuran, thf）配合物均为单体结构，多数呈现13配位构型，每个DMADB配体通过四个B–H···Ln桥键与金属中心螯合（每个BH₃基团为κ²H配位模式，即形成两个B–H···Ln相互作用）。对于体积最小的三种镧系元素——铥、镱和镥，其金属中心为12配位，因为其中一个DMADB配体仅通过三个B–H···Ln桥键与金属中心螯合。无碱型Ln(H₃BNMe₂BH₃)₃配合物的结构高度依赖于镧系离子的半径：随着离子半径减小，配位数从14（镨）降至13（钐），再降至12（镝、钇、铒）。14配位配合物为聚合型结构：每个金属中心与两个螯合型DMADB配体结合，同时与两个以Ln(κ³H-H₃BNMe₂BH₃-κ³H)Ln模式桥连的配体的两个末端位点结合。在13配位配合物中，全部三个DMADB配体均为螯合配位，但金属原子同时还与相邻分子的一个氢原子配位。12配位配合物呈双核结构，每个金属中心与两个螯合型DMADB配体结合，同时与两个以Ln(κ²H-H₃BNMe₂BH₃-κ²H)Ln模式桥连的配体的两个末端位点结合。该类配合物可与水发生反应，部分水解产物[La(H₃BNMe₂BH₃)₂(OH)]₄的结构中，镧原子与氧原子构成畸变立方骨架；每个镧原子与三个桥连羟基相连，并结合两个螯合型DMADB配体，每个螯合型DMADB配体的一条B–H键可与相邻金属中心形成桥连作用。所有配合物均已测定场电离质谱数据、熔点与分解温度、热重分析数据以及核磁共振（NMR）数据，其中包括顺磁性镧系诱导位移（paramagnetic lanthanide induced shifts, LIS）的分析。Ln(H₃BNMe₂BH₃)₃类化合物具有高挥发性，可在低至65℃的真空环境下升华，适合用作制备薄膜的化学气相沉积（chemical vapor deposition, CVD）与原子层沉积（atomic layer deposition, ALD）前驱体。
