The invention comprises as new compounds nitrogen bridged (5,2,1,02,6)-8-alkenes in which the nitrogen bridge links the carbon atoms in positions 3 and 5, the bridge being composed solely of two nitrogen atoms which are directly linked by a double or single bond. These may be represented by the general formula <FORM:0789113/IV (b)/1> in which the unsatisfied valencies (not shown) may be satisfied by various groups. They may be prepared by causing derivatives of azodicarboxylic acid, especially its esters, amides or amidines, to react by 1,4-addition with a conjugated cyclopentadiene hydrocarbon and then reacting the resulting intermediate compound with a second molecule of a cyclopentadienoic compound to give a nitrogen-bridged tricyclo(5,2,1,02,6)-8-decene in which the two nitrogens of the nitrogen bridge are substituted by formic ester, carboxamido, carboxamidino or other groups depending on the azodicarboxylic acid derivative used as starting material. The products can be converted to the corresponding compounds in which the exocyclic bond of at least one of the two nuclear nitrogens is satisfied by hydrogen. When both of the nitrogen atoms are attached to hydrogen atoms the compounds may be oxidized to give products in which the nitrogen atoms are connected by a double bond. The process of preparation may be represented as follows:- <FORM:0789113/IV (b)/2> in which R is an ester group, a carboxamido group, a carboxamidino group or a carboxamidino salt group. Suitable esters of azodicarboxylic acid which may be used are aliphatic, aromatic, cycloaliphatic or mixed esters. Suitable amides are azoformamide and its N-substituted derivatives. The corresponding amidines such as azodicarboxylic diamidine, NH2C(NH)N=NC(NH)NH2, and its alkyl derivatives may be used. As the cyclopentadiene hydrocarbon reacted first there may be used 1,3-cyclopentadiene or its derivatives containing one or more alkyl substituents containing up to 4 carbon atoms. As the cyclopentadiene compound reacted with the intermediate compound there may be used a cyclopentadiene having one or more substituent groups, preferably halogen groups. The first step may be carried out by mixing the azodicarboxylic acid derivative with the conjugated cyclopentadiene hydrocarbon at temperatures preferably between 0 DEG and 25 DEG C. A solvent may be used. The second step is carried out by heating the intermediate compound with the cyclopentadiene compound preferably in the presence of a polymerization inhibitor. When the cyclopentadiene compound contains halogen substituents, small amounts of hydrogen halide may be formed and an acid-scavenger, such as an oxirane compound, should preferably be added to neutralise the liberated acid. Substitution of hydrogen for the ester groups attached to the nuclear nitrogen atoms may be carried out by heating in the presence of a strong acid or strong alkali. Decarboxamidation and decarboxamidination may be accomplished by heating the N-substituted compound with water, preferably in the presence of mineral acid or an alkali as catalyst. The unsubstituted hydrazo compounds may be used for the preparation of other derivatives. For example, by reacting with acid halides or acid anhydrides 4-acetyl-1,8,9,10,11,11-hexachloro - 4,5 - diazatetracyclo - (6,2,1,13,6,02,7) - 9-dodecene and 4,5-dipropionyl-1,8,9,10,11,11-hexachlor - 4,5- diazatetracyclo - (6,2,1,13,6,02,7)-9-decene; by reaction with alkyl halide 4,5-dimethyl - 1,8,9,10,11,11 - hexachloro - 4,5 - diazatetracyclo-(6,2,1,13,6,O2,7)-9-dodecene and similar compounds be obtained; by reaction with nitrosyl halides compounds such as 4-nitroso1,8,9,10,11,11 - hexachloro - 4,5 - diazatetracyclo - (6,2,1,13,6,02,7) - 9 - dodecene are obtained; N-aryl, N,N-diaryl and mono- and dinitramine compounds may also be obtained. The azo compounds of the invention can be converted to azoxy compounds such as 1,8,9,10,11,11 - hexachloro - 4,5 - diazatetracyclo - (6,2,1,13,6,02,7) - 4,9 - dodecadiene - 4 - oxide by peroxidation with peracids such as perbenzoic acid, peracetic acid and persuccinic acid. In the examples the preparation of (a) 4,5-dicarbethoxy - 1,8,9,10,11,11 - hexachloro - 4,5 - diazatetracyclo - (6,2,1,13,6,02,7) - 9 - dodecene; (b) 4,5 - dicarbomethoxy - 1,8,9,10,11,11 - hexachloro - 4,5 - diazatetracyclo - (6,2,1,13,6,02,7) - 9-dodecene; (c) 4,5-dicarbobutoxy-1,8,9,10,11,11 - hexachloro - 4,5 - diazatetracyclo - (6,2,1,13,6,02,7) - 9 - dodecene; (d) 1,8,9,10,11,11 - hexachloro - 4,5 - diazatetracyclo - (6,2,1,13,6,02,7) - 9 - dodecene hydrochloride; (e) 1,8,9,10,11,11 - hexachloro - 4,5 - diazatetracyclo - (6,2,1,13,6,02,7) - 9 - dodecene sulphate; (f) 4 - carbethoxy - 1,8,9,10,11,11 - hexachloro - 4,5 - diazatetracyclo - (6,2,1,13,6,02,7) - 9 - dodecene; (g) 1,8,9,10,11,11 - hexachloro - 4,5 - diazatetracyclo - (6,2,1,13,6,02,7) - 4,9 - dodecadiene; (h) 1,8,9,10,11,11 - hexachloro - 4,5 - diazatetracyclo - (6,2,1,13,6,02,7) - 4,9 - dodecadiene; and (j) 1,8,9,10,11,11 - hexachloro - 4,5 - diazatetracyclo - (6,2,1,13,6,02,7) - 4,9 - dodecadiene - 4 - oxide is described.ALSO:Nitrogen bridged tricyclo-(5,2,1,02, 6)-8-alkenes, in which the nitrogen bridge links the carbon atoms in positions 3 and 5 and consists of two nitrogen atoms linked with a single or double bond, may be used as insecticides and fungicides; they may be used as a mixture with a horticultural carrier and/or a surface-active agent or as a solution in solvents such as water or aqueous alcohols with the addition of a wetting agent, if desired. The polycyclic compounds have the structure <FORM:0789113/VI/1> the unsatisfied valencies (not shown) being satisfied by hydrogen or groups such as alkyl, carboxy and halogen. The acid addition salts may also be used. For example, the compounds 1,8,9,10,11,11 - hexachloro - 4,5 - diazatetracyclo - (6,2,1,13,6.O2,7) - 9 - dodecene hydrochloride and 1,8,9,10,11,11-hexachloro-4,5-diazatetracyclo - (6,2,1,13,6,02,7) - 9 - dodecene sulphate may be employed in solution and an alkali may be added to the solution to liberate the free hydrazo base. Insecticidal dusts may be prepared by absorbing the compounds on solid carriers such as clays, calcium carbonate, silica, and wood flours. The new insecticides may be used also in conjunction with known insecticides. In an example the effectiveness of the following new insecticides in acetone solution is tested against various insects:-(a) 1,8,9,10,11,11 - hexachloro - 4,5 - diazatetracyclo - (6,2,1,13,6,02,7) - 9 - dodecene hydrochloride; (6) 4 - carbethoxy - 1,8,9,10,11,11-hexachloro-4,5-diazatetracyclo-(6,2,1,13,6, 02,7)-9 - dodecene; (c) 4,5 - dicarbomethoxy - 1,8,9,10,11,11 - hexachloro - 4,5 - diazatetracyclo - (6,2,1,13,602,7) - 9 - dodecene; (d) 4,5 - dicarbethoxy - 1,8,9,10,11,11 - hexachloro - 4,5 - diazatetracyclo - (6,2,1,13,6,02,7) - 9 - dodecene; (e) 1,8,9,10,11,11 - hexachloro - 4,5 - diazatetracyclo - (6,2,1,13,6,02,7) - 4,9 - dodecadiene; (f) 4-carbomethoxy - 1,8,9,10,11,11 - hexachloro - 4,5-diazatetracyclo - (6,2,1,13,6,02,7) - 9 - dodecene; (g) 1,8,9,10,11,11 - hexachloro - 4,5 - diazatetracyclo - (6,2,1,13,6,02,7) - 9 - dodecene sulphate and (h) 1,8,9,10,11,11-hexachloro-4,5-diazatetracyclo-(6,2,1,13,6, 02,7)-4,9-dodecadiene-4-oxide.