Try applying the functions directly to your character vector:
stemDocument(dicBin, language="german")
stripWhitespace(dicBin)
tolower(dicBin)
To transform a corpus back to a character vector, try
as.character(dicBin.corp)
# [1] "rosa" "rosig" "grun" "blau" "gelb" "lila" "orang"
# [8] "pink" "%" "mm" "mp" "*" "monat"