Gallium Triorganyls
The reaction of methyl Grignard reagents with gallium halides leads to the etherate Ga(CH3)3-O(C2H5)2 [1,2] which can be converted into solvent-free Ga(CH3)3 by heating in a higher boiling ether [22]. The preparation of solvent-free Ga(CH3)3 from GaCl3 an
- PDF / 11,892,748 Bytes
- 120 Pages / 505 x 720 pts Page_size
- 63 Downloads / 159 Views
Compounds of the GaR3 Type
1.1;1
Trimethylgallium and Its Adducts
1.1.1.1 1.1.1.1.1
Ga(CH 3)3 Preparation
The reaction of methyl Grignard reagents with gallium halides leads to the etherate Ga(CH 3h' O(C2HSh [1, 2] which can be converted into solvent-free Ga(CH3)3 by heating in a higher boiling ether [22]. The preparation of solvent-free Ga(CH3b from GaCl3 and CH 3MgI in O(C sH,,-i)2 in a 68% yield has been claimed in (44). The Grignard solution containing an excess of CH31 can alsO be electrolyzed using a Ga-pool anode and a Pt cathode to give Ga(CH 3h' O(C 2Hs)2 which is converted into Ga(CH3h by addition of O(C sH,,-i)2' removal of ether under vacuum, and decomposition of Ga(CH 3h'O(CsH,,-i)2 at 190°C [40); see also (45). Other alkylating organometallics have been'used to directly obtain the solvent-free compound. The reaction of excess GaCl3 with Zn(CH 3)2 vapor in a vacuum apparatus is violent in the initial stages where partially alkylated products are formed, but heating to 80 to 120°C results in complete alkylation to give Ga(CH 3h in a practically quantitative yield. The appearance of Ga(CH3h can easily be detected since it crystallizes at -33°C from even considerable quantities of unreacted Zn(CH 3h [1). For the separation of Ga(CH3h from possibly remaining Zn(CH 3h special equipment for isothermal reflux distillation below room temperature has been recommended to be more suited than the usual fractional vacuum condensation [13). The preparation from GaCl3 by controlled slow addition of excess Al(CH 3b [25) (extremely exothermic reaction) is described in detail in (11). The crude product is distilled from the reaction mixture onto NaF and redistilled from NaF in order to remove any Al(CH3)2Cl (63% yield) (11); see also [7). Yields of 55 to 58% were obtained with 3 to 4 molar equivalents of Al(CH 3h, while 2 molar equivalents gave only a yield of 10 to 12% [8). A preparation in the presence of KCl has been claimed [6). Both purity and yield of Ga(CH3b are improved by using n-hexane or n-heptane as displacing agents during the distillative separation of Ga(CH3b from Al(CH 3h and other reaction products [9,10]. The impurity content could be reduced from 10-2 to 10-s wt% [9]. Based on model concepts calculations were made to determine several parameters of this stepwise alkylation reaction (12). Yields of 90 to 95% have been reported for the preparation from GaBr3 and Al(CH 3b [4,5) at 140°C, with continuous distillation of Ga(CH 3b. GaBr3 is used as a solid or is first dissolved in Al(CH 3hBr which results in a strongly exothermic reaction [5). The alkylation of GaCl3 with Na[Ga(CH 3)4) (1:3 mole ratio) occurred with heating and continuous dilution of the reaction mixture to give a 70% yield of Ga(CH3h after distillation [20). The preparation from GaC~ or GaBr3 and LiCH 3 was only briefly mentioned (3). Ga(CH3b also forms in the reaction of Ga-Mg (2: 3) alloys with CH31 in ether solvents, e.g., in THF (38% yield) and in O(C4H9h or O(C sH,,-i)2 (50 to 55% yield). The highest yield of 95% was reported for
Data Loading...
