Tantalum and niobium compounds having the general formula (I) and their use for the chemical vapour deposition process are described: ##STR00001## wherein M stands for Nb or Ta, R.sup.1 and R.sup.2 C.sub.1 to C.sub.12 alkyl, C.sub.5 to C.sub.12 cycloalkyl, C.sub.6 to C.sub.10 aryl radicals, 1-alkenyl, 2-alkenyl, 3-alkenyl, triorganosilyl radicals --SiR.sub.3, or amino radicals NR.sub.2 R.sup.3 is C.sub.1 to C.sub.8 alkyl, C.sub.5 to C.sub.10 cycloalkyl, C.sub.6 to C.sub.14 aryl radical, or SiR.sub.3 or NR.sub.2, R.sup.4 denotes Cl, Br, I, NIH--R.sup.5 where R.sup.5 is C.sub.1 to C.sub.8 alkyl, C.sub.5 to C.sub.10 cycloalkyl or C.sub.6 to C.sub.10 aryl radical, or O--R.sup.6 where R.sup.6=optionally substituted C.sub.1 to C.sub.11 alkyl, C.sub.5 to C.sub.10 cycloalkyl, C.sub.6 to C.sub.10 aryl radical, or --SiR.sub.3, or BH.sub.4, or an allyl radical, or an indenyl radical, or an benzyl radical, or an cyclopentadienyl radical, or --NIR--NR'R'' (hydrazido(-1), wherein R, R' and R'' have the aforementioned meaning of R, or CH.sub.2SiMe.sub.3, pseudohalide, or silylamide --N(SiMe.sub.3).sub.2, and R.sup.7 and R.sup.8 are H, C.sub.1 to C.sub.12 alkyl, C.sub.5 to C.sub.12 cycloalkyl or C.sub.6 to C.sub.10 aryl radicals.