the new tellurium ( ii ) compound ( 1 ) and the preferred complexes ( 2 ) and ( 3 ) of the present invention can be represented by the formulae : the integer n can be from 1 to 10 , and the integer m is from 1 to 3 . while alkylene chains longer than 10 carbon atoms are useful for some purposes , compounds having shorter alkylene chains tend to be more soluble in nonpolar organic solvents . thus , a lower alkylene , i . e ., when n is from 1 to 4 , is preferred , particularly when n is equal to 1 . similarly , while r , r &# 39 ; and r &# 34 ; can be either alkyl having , for example , 1 to 10 carbon atoms such as methyl , ethyl , isopropyl or aryl such as phenyl including substituted aryl or multiple ring aromatic groups such as napthyl , smaller groups such as phenyl are preferred because they tend to increase solubility . r , r &# 39 ; and r &# 34 ; can also be heterocyclic groups . useful heterocyclic radicals include thiazoles , isoxazoles , benzothiazoles , benzoxazoles , phenyloxazoles and the like . again , smaller groups are preferred . at least two of r , r &# 39 ; and r &# 34 ; are preferably lower alkyl , particularly methyl . the anion x in the copper and palladium complexes described above can be halogen such as chlorine , bromine and iodine or a pseudohalogen . pseudohalogens are anions which have properties very similar to halogens such as scn - , nco - , ncse - , ncte - and the like . in the copper complexes , m can be an integer from 1 to 3 . the exact value of m depends on the coordination number assumed by the copper atom of the complex . the described diorganotellurium ( ii ) compounds and their transition metal complexes are soluble in nonpolar organic solvents . by &# 34 ; soluble &# 34 ; is meant that it is possible to form at least a 0 . 1 m solution of the tellurium ( ii ) compound or complex in the selected solvent at room temperature . typically , however , the preferred compounds are more soluble and 1 . 0 m solutions of the compounds are possible in nonpolar organic solvents at room temperature . typical nonpolar organic solvents include ethers such as dimethyl ether , diethyl ether and the like ; saturated hydrocarbons including hexane , cyclohexane ; and other common organic solvents . the new diorganotellurium ( ii ) compounds of the present invention can be prepared by a two - step reaction sequence . in the first step , elemental tellurium is reduced to tellurium ( 2 -). this can be accomplished , for example , by reacting tellurium metal with a reducing agent such as potassium borohydride in an aqueous solution of sodium hydroxide . in the second step , the tellurium ( 2 -) is reacted with two equivalents of the appropriate silicon - containing alkyl halide in an alcohol solution . because the tellurium ( 2 -) is extremely air - sensitive , these steps should be carried out in an inert atmosphere such as nitrogen or argon . after refluxing the tellurium ( 2 -) and silicon - containing alkyl halide solution for a time sufficient to complete the reaction , typically 3 -- 20 hours , the alcohol is distilled from the solution . the diorganotellurium ( ii ) is then extracted from the aqueous solution with a suitable solvent such as ethyl ether . the resulting diorganotellurium ( ii ) is a liquid at room temperature and can be purified by conventional methods such as by vacuum distillation . alkyl halides containing the necessary tertiary silicon atom are known in the art . examples of useful silicon - containing alkyl halides include ( ch . sub . 3 ) 3 sich 2 ch 2 ch 2 cl , c 6 h 5 ( ch 3 ) 2 sich 2 cl , [( ch 3 ) 3 - si ] 2 chcl , ( c 2 h 5 ) 3 sich 2 cl and the like . the transition metal complexes of the diorganotellurium ( ii ) compounds of the present invention can be prepared by known methods . useful methods are described , for example , in u . s . pat . no . 3 , 859 , 092 and by m . r . collier et al , j . chem . soc . ( dalton ), 445 ( 1973 ). for example , copper ( i ) diorganotellurium ( ii ) complexes can be prepared by reacting the proper copper ( i ) halide with a diorganotellurium ( ii ) compound of the invention in a solution of chloroform or methylene chloride . palladium complexes of the diorganotellurium ( ii ) compounds of the present invention are conveniently prepared by a substitution reaction by using the appropriate palladium complex which is coordinated to labile ligands . useful palladium complexes for this substitution reaction include k 2 pd ( scn ) 4 , k 2 pdcl 4 , k 2 pd ( c 2 o 4 ) 4 and pdcl 2 ( ncc 6 h 5 ) 2 . a preferred embodiment of the present invention is an image - forming combination comprising ( i ) the described tellurium ( ii ) compound or complex as an oxidizing agent and ( ii ) a reducing agent . the image - forming combination can be in a solvent , which can be a nonpolar organic solvent , thereby forming a physical developer solution . alternatively , the image - forming combination can be on a suitable support either alone or with other components including light - sensitive components , other oxidants , binders and the like . suitable methods of making and using the present image - forming combination can be found in copending , commonly assigned u . s . applications ser . nos . 848 , 062 and 848 , 063 filed nov . 3 , 1977 . because of their desirable solubility properties , the image - forming combination of the present invention can be used with , and coated from , nonpolar organic solvents . suitable solvents of this type are described above in relation to the solubility of the present compounds . because the transition metal complexes described above are light - sensitive , they can be coated , using nonpolar organic solvents , onto or imbibed into suitable photographic supports to provide useful photographic elements . the complexes can be used individually or mixtures of two or more of the complexes can be used . a photosensitive element can be prepared by soaking porous paper in a solution containing the transition metal complex of the diorganotellurium ( ii ) compound of the present invention . the paper is then dried , thereby producing a photosensitive element . if desired , the compound can be added to a binder solution and coated onto a substrate by any means , such as dip coating , brushing , rolling , spraying , hopper coating or the like . the binder used as a vehicle for the photosensitive complex can be any of the hydrophilic binders used in photographic elements , including natural materials such as gelatin , albumin , agar - agar , gum arabic , alginic acid , etc ., and synthetic materials such as poly ( vinyl alcohol ), poly ( vinyl pyrrolidone ), cellulose esters , partially hydrolyzed cellulose acetate and the like . because the complexes are soluble in nonpolar organic solvents , polymers which are soluble in these solvents can be used as binders . typical binders of this type include polystyrene , poly ( vinyl butyral ) and cellulose acetate butyrate . it is noted that , although many binders may be used herein , the binder should be permeable to the developer used if a solution is used to process the element . the binder should not absorb appreciably in the region of sensitivity of the compound . the compound may be used with varying amounts of binder material . preferably , the compound - to - binder weight ratio is from about 3 : 1 to about 1 : 2 . the complex can be either imbibed into or coated onto any support typically used for photographic elements . support materials used herein are subject to wide variation . glass can be used as can be metals such as aluminum , copper , zinc and tin . conventional film bases such as cellulose acetate , cellulose nitrate , cellulose acetate butyrate , poly ( ethylene terephthalate ), polystyrene and paper , including polyethylene - coated paper and polypropylene - coated paper , can also be used . if the compound is to be imbibed into the support , porous materials such as uncoated paper should be used . the elements having the described complexes thereon are typically exposed through a pattern of actinic radiation to provide a latent image corresponding to the exposed areas . the transition metal complexes of the present invention are sensitive to actinic radiation such as ultraviolet rays generally in the wavelength range of 1800 to 4000 angstroms . many sources of ultraviolet light may be used such as high - pressure mercury vapor lamps , carbon arc lamps , and the like . some of these complexes are also sensitive to electron - beam exposure , as well as exposure to neutrons and α - particles . as used herein , &# 34 ; electromagnetic radiation &# 34 ; is intended to include all of these forms of energy . in some instances , the rate of development of the described photosensitive element can be considerably accelerated by heating the exposed elements prior to treatment with a physical developer . thus , a shorter exposure time to achieve a developable image can be used if the element is heated after exposure and prior to development . in some cases , exposed photosensitive complexes of the present invention will &# 34 ; print out &# 34 ; by the application of heat after imagewise exposure . generally , the element can be heated to about 100 ° c . to about 200 ° c . for about 1 to about 60 seconds to exhibit these effects . after imagewise exposure , an element having a layer containing a complex of the present invention has an imagewise distribution of catalytic transition metal nuclei . by &# 34 ; nuclei &# 34 ; is meant small calalytic specks of elemental metal . this imagewise distribution can be physically developed by contacting the layer with a redox image - forming combination using any of a wide variety of methods . a particularly suitable method is simply to immerse the element into a physical developer bath . alternatively , the catalyst layer can be overcoated with a viscous physical developer solution . in still another method , the catalyst layer can be contacted with a dry amplification element containing a suitable physical developer composition . the physical developer composition itself generally contains the reactants for a redox reaction . either the oxidizing agent or the reducing agent can be the image - forming material . the development can use either the change in electromagnetic radiation absorption or the change in solubility of the image - forming material that takes place as a result of the redox reaction . a typical physical developer composition contains the salt of a heavy metal ion , a complexing agent for the ion and a reducing agent for the ion . useful heavy metal salts include silver salts , cupric salts , palladium salts , tellurium salts ( including the compounds of the present invention ) and nickel salts . the physical developer can also contain a variety of other materials . useful additives include acids and bases to adjust ph , buffers , preservatives , thickening agents , brighteners , surfactants and the like . another type of physical developer produces a dye image . these developers typically contain a reducible dye precursor and a reducing agent . physically developable catalysts having deposits of a phthalocyanine or a formazan dye are autocatalytic . the following references relate to the described and other physical development compositions and processes : u . s . pat . nos . 3 , 223 , 525 , 3 , 253 , 923 , 3 , 390 , 998 , 3 , 576 , 631 , 3 , 578 , 449 , 3 , 591 , 609 , 3 , 650 , 748 , 3 , 512 , 972 , 3 , 893 , 857 , 3 , 935 , 013 , 4 , 042 , 392 and 4 , 046 , 569 ; british pat . no . 1 , 125 , 646 ; research disclosure , 15631 ; hornsby , basic photographic chemistry ( 1956 ), 66 ; and mees and james , the theory of the photographic process , 3rd ed . ( 1966 ), pp . 329 - 331 . all of these references are hereby incorporated by reference . particularly useful heavy metal physical development baths include the copper enplate developer baths ( a trademark of enthone inc .) containing copper sulfate , formaldehyde , rochelle salt and nickel sulfate . where the element is processed by overcoating the element with the physical developer composition , the overcoat can be any of a wide variety of heat - activatable compositions . these compositions are described , for example , in u . s . pat . nos . 3 , 152 , 904 , 3 , 330 , 678 and 3 , 392 , 020 , british pat . nos . 1 , 110 , 046 , 1 , 131 , 108 , 1 , 161 , 779 , 1 , 342 , 523 and 1 , 346 , 252 , and german pat . no . 888 , 045 , all of which are hereby incorporated by reference . the overcoat can be coated on the element by any means such as those useful for coating the light - sensitive complexes . the heat - activatable physical developer compositions can comprise a source of silver ion , which is believed to be an oxidizing agent which reacts with a reducing agent , the reaction being catalyzed by the physically developable nuclei . the oxidizing agent , which is preferably a silver salt , should be resistant to darkening under illumination to prevent undesired deterioration of a developed image . preferably , the silver salt oxidizing agent is a long - chain fatty acid . as employed herein , &# 34 ; long - chain &# 34 ; is intended to mean a chain of carbon atoms containing at least 10 carbon atoms , typically 10 - 30 carbon atoms . an especially useful class of silver salt oxidizing agents is the silver salt of long - chain fatty acids containing at least 20 carbon atoms . compounds which are useful silver salts of long - chain fatty acids are , for example , silver behenate , silver stearate , silver oleate , silver laurate , silver hydroxystearate , silver caprate , silver syristate , silver palmitate and the like . other silver salt oxidizing agents which are useful in the present invention include silver benzoate , silver phthalate , silver acetate , silver acid phthalate and the like ; silver phthalazinone , silver benzotriazole , silver saccharin and the like . a particularly useful source of silver ion is a dispersion of the silver complex of the ligand 3 - carboxy - methyl - 4 - methyl - 4 - thiazoline - 2 - thione . the dispersion of this complex with a reducing agent to form a heat - activatable physical developer composition is described in u . s . pat . no . 3 , 785 , 850 issued jan . 15 , 1974 , the disclosure of which is hereby incorporated by reference . the following examples are presented to illustrate the invention and not to limit it in any way . example 1 : synthesis of te -- ch 2 ch 2 ch 2 si ( ch 3 ) 3 ] 2 potassium borohydride ( 44 . 7 g , 0 . 828 mole ) was added to 700 ml of a 20 % aqueous sodium hydroxide solution in a 2 - liter , 3 - neck flask fitted with a reflux condenser , dropping funnel and argon - gas inlet tube . the solution was deaerated with argon and then tellurium metal ( 42 . 2 g , 0 . 331 g - atom ; alfa products tellurium shot , 3 . 2 mm , m6n ) was added . the resulting suspension was refluxed under argon for 2 . 5 hr to give a clear yellow solution . to this solution of tellurium ( 2 -) was added a deaerated solution of ( ch 3 ) 3 sich 2 ch 2 ch 2 cl ( 100 g , 0 . 662 mole ) in 800 ml of methanol . the reaction solution was refluxed 20 hr and thereafter the methanol was distilled off . the residual solution was then extracted with two 1 - liter ethyl ether portions . the combined ether extracts were washed with water , dried over magnesium sulfate and the ether distilled off to give a pale orange liquid ( 113 g , 95 . 6 %). the crude telluride was purified by vacuum distillation . the title compound was confirmed by elemental analysis . elemental analysis , boiling point and index of refraction for the title compound and other compounds prepared in an analogous manner are presented in table 1 . table 1______________________________________elemental analysis calc &# 39 ; d . ( found ) compound c h te bp n . sub . d . sup . 20______________________________________te [ ch . sub . 2 si ( ch . sub . 3 ). sub . 3 ]. sub . 2 31 . 81 7 . 34 42 . 25 66 - 1 . 5007 ( 28 . 5 ) ( 6 . 8 ) ( 42 . 3 ) 68 ° te [ ch . sub . 2 si ( ch . sub . 3 ). sub . 2 c . sub . 6 h . sub . 5 ]. sub . 2 50 . 79 6 . 15 29 . 94 103 - 1 . 5880 ( 49 . 3 ) ( 6 . 7 ) ( 29 . 8 ) 104 ° te [ ch . sub . 2 ch . sub . 2 ch . sub . 2 si ( ch . sub . 3 ). sub . 3 ]. sub . 2 40 . 24 8 . 44 35 . 63 52 ° 1 . 4988 ( 40 . 0 ) ( 8 . 7 ) ( 34 . 9 ) ______________________________________ method a : pdcl 2 { te -- ch 2 si ( ch 3 ) 3 ] 2 } 2 to a solution of 3 . 2 g ( 10 mmoles ) pdcl 2 ( ncc 6 h 5 ) 2 ( prepared as described by m . s . kharasch et al , j . amer . chem . soc ., 60 , p . 882 ( 1938 )) in 250 ml of benzene were added 3 . 2 g ( 10 mmoles ) of te [ ch 2 si ( ch 3 ) 3 ] 2 . the reaction solution , after stirring at room temperature for 1 hr , was concentrated to dryness and the residue was recrystallized from 175 ml 4 : 1 methanol - hexane to give , on cooling to - 10 ° c ., a crop of orange needles . the title complex was confirmed by elemental analysis . method b : pdcl 2 { te -- ch 2 ch 2 ch 2 si ( ch 3 ) 3 ] 2 } 2 to a solution of 1 . 6 g ( 5 mmoles ) of k 2 pdcl 4 ( prepared as described in gmelin &# 39 ; s handbuch der anorganischen chemie , 68 , p . 83 ( 1938 )) in 150 ml of water was added a solution of 3 . 6 g ( 10 mmoles ) te [ ch 2 ch 2 ch 2 si ( ch 3 ) 3 ] 2 in 150 of methanol . a red precipitate immediately formed . the reaction solution was stirred at room temperature for 15 min , filtered and the crude product washed well with water , ethanol and air - dried . the product was recrystallized from 4 : 1 methanol - hexane to give 3 . 2 g of orange crystals . the title complex was confirmed by elemental analysis . the melting point was 70 ° c . both palladium dichloride complexes described above easily formed 1 . 0 m solutions in diethyl ether . example 3 : synthesis of pd ( scn ) 2 { te -- ch 2 si ( ch 3 ) 3 ] 2 } 2 to a solution of 2 . 6 g ( 6 mmoles ) of k 2 pd ( scn ) 4 ( prepared as described by n . j . destefano and j . l . burmeister , syn . inorg . metal - organic chem ., 3 , p . 313 ( 1973 )) in 400 ml methanol were added 3 . 6 g ( 12 mmoles ) of te [ ch 2 si ( ch 3 ) 3 ] 2 . the reaction solution was stirred 60 min at room temperature and then concentrated to dryness under vacuum . the crude red product was recrystallized from 120 ml 4 : 1 methanol - hexane to give 4 . 3 g of bright red crystals . the title complex was confirmed by elemental analysis . the melting point was 143 ° c . example 4 : synthesis of cubr { te -- ch 2 ch 2 ch 2 si ( ch 3 ) 3 ] 2 } 2 to a solution of 11 . 5 g ( 32 moles ) te -- ch 2 ch 2 ch 2 si ( ch 3 ) 3 ] 2 , prepared as described in example 1 , in 500 ml trichloromethane were added 2 . 25 g ( 15 . 7 mmoles ) of solid cubr ( prepared as described in inorg . synth ., 2 , p . 3 ( 1946 )). the reaction solution was stirred at room temperature for 10 hr and then the solvent was removed under vacuum to give a white residue . the residue was washed with 100 ml methanol at room temperature and then recrystallized from 500 ml hot methanol to give 5 g of pure product as white needles . the title complex was confirmed by elemental analysis . the melting point was 55 ° c . example 5 : photosensitivity of pdcl 2 { te -- ch 2 ch 2 ch 2 si ( ch 3 ) 3 ] 2 } 2 a solution of 100 mg of pdcl 2 { te -- ch 2 ch 2 ch 2 si ( ch 3 ) 3 ] 2 } 2 ( prepared as described in example 2 - b ) in 10 ml dichloromethane was imbibed in paper stock and imagewise - exposed for 60 sec under a high - pressure mercury arc . immersion of this exposed paper in an aqueous dye physical developer ( 5 % in triphenyltetrazolium chloride and 1 % in hydrazine ) gave a red negative image of the corresponding formazan dye . example 6 : photothermographic property of cubr { te -- ch 2 ch 2 ch 2 si ( ch 3 ) 3 ] 2 } 2 a solution containing 100 mg of the title complex ( prepared as described in example 4 ) dissolved in 10 ml of dichloromethane was imbibed into paper stock . a 30 - sec imagewise exposure of this sensitized paper stock under a 360 - watt high - pressure mercury arc resulted in a faint yellow printout . subsequent heating of the exposed paper for 10 sec at 175 ° c . produced a grey - black negative image . example 7 : the use of cubr { te -- ch 2 ch 2 ch 2 si ( ch 3 ) 3 ] 2 } 2 as an oxidant in dry physical development a dry element was prepared by dissolving 100 mg of cubr { te -- ch 2 ch 2 ch 2 si ( ch 3 ) 3 ] 2 } 2 ( as an oxidant ) and 120 mg of 2 , 6 - dichloro - 4 - benzenesulfonamidophenol ( as a reducing agent ) in 10 ml of a 7 % solution of poly ( vinyl butyral ) in a 1 : 1 solution of acetone and toluene . the resulting image - forming combination was coated at 10 mils wet thickness onto a subbed poly ( ethylene terephthalate ) support to form an amplification element . this element was laminated to a second piece of poly ( ethylene terephthalate ) on which a step tablet distribution of nuclei of palladium had been vacuum - evaporated so that the image - forming combination was in contact with the palladium . passing of the laminate through heated rollers at 175 ° c . resulted in selective copper amplification of the palladium nuclei down to a coverage of 3 . 94 × 10 - 14 atoms / cm 2 . the invention has been described in detail with particular reference to preferred embodiments thereof , but it will be understood that variations and modifications can be effected within the spirit and scope of the invention .